Add a StdoutTransport

A common pattern is to "log" exceptions and messages to Sentry. It's a
convenient place to collect programmer errors: situations that
absolutely should not happen according to the business logic, but happen
anyway because of constraints not caught by the type system or test
suite.

In debug builds we often have Sentry disabled because we don't want to
clutter it with all the ANRs and simple mistakes of development life.
This can mean that exceptions we are "logging" to Sentry get missed.

Instead we can use a `StdoutTransport`, logging them to the stdout log:

```kotlin
SentryAndroid.init(this) { options ->
    if (BuildConfig.DEBUG) {
        options.setTransport(StdoutTransport(options.serializer))
    }
}
```

This will log a message like so:

```
03-20 18:32:47.623 17385-17436/io.sentry.sample I/System.out: {"breadcrumbs":[],"contexts":{"app":{"app_build":"1","app_identifier":"io.sentry.sample","app_version":"1.0"},"os":{"build":"sdk_google_phone_x86-userdebug 6.0 MASTER 5525988 test-keys","kernel_version":"Linux version 3.10.0+ (lfy@lfy0.mtv.corp.google.com) (gcc version 4.9 20140827 (prerelease) (GCC) ) #1 SMP PREEMPT Wed Feb 22 08:53:42 PST 2017","name":"Android","rooted":true,"version":"6.0"},"device":{"arch":"x86","archs":["x86"],"battery_level":100.0,"boot_time":"2020-03-17T19:59:39Z","brand":"Android","charging":true,"external_free_storage":534726656,"external_storage_size":534761472,"family":"Android","free_memory":1231368192,"free_storage":346652672,"id":"7db661d77068d2d8","language":"en_US","low_memory":false,"manufacturer":"unknown","memory_size":1588129792,"model":"Android SDK built for x86","model_id":"MASTER","name":"Android SDK built for x86","online":true,"orientation":"portrait","screen_density":3.0,"screen_dpi":480,"screen_height_pixels":1776,"screen_resolution":"1776x1080","screen_width_pixels":1080,"simulator":true,"storage_size":812531712,"timezone":"GMT"}},"dist":"1","event_id":"bb32506411d94d40b042a8a3862f6d43","exception":{"values":[{"module":"java.lang","stacktrace":{"frames":[{"native":false,"filename":"ZygoteInit.java","function":"main","in_app":false,"lineno":616,"module":"com.android.internal.os.ZygoteInit"},{"native":false,"filename":"ZygoteInit.java","function":"run","in_app":false,"lineno":726,"module":"com.android.internal.os.ZygoteInit$MethodAndArgsCaller"},{"native":true,"filename":"Method.java","function":"invoke","in_app":false,"module":"java.lang.reflect.Method"},{"native":false,"filename":"ActivityThread.java","function":"main","in_app":false,"lineno":5417,"module":"android.app.ActivityThread"},{"native":false,"filename":"Looper.java","function":"loop","in_app":false,"lineno":148,"module":"android.os.Looper"},{"native":false,"filename":"Handler.java","function":"dispatchMessage","in_app":false,"lineno":95,"module":"android.os.Handler"},{"native":false,"filename":"Handler.java","function":"handleCallback","in_app":false,"lineno":739,"module":"android.os.Handler"},{"native":false,"filename":"View.java","function":"run","in_app":false,"lineno":21147,"module":"android.view.View$PerformClick"},{"native":false,"filename":"View.java","function":"performClick","in_app":false,"lineno":5198,"module":"android.view.View"},{"native":false,"filename":"lambda","function":"onClick","in_app":true,"module":"io.sentry.sample.-$$Lambda$MainActivity$tVGPRGxxb8SivUa5SKhzp6BuXOI"},{"native":false,"filename":"MainActivity.java","function":"lambda$onCreate$2","in_app":true,"lineno":32,"module":"io.sentry.sample.MainActivity"}]},"thread_id":1,"type":"Exception","value":"java.lang.Exception: java.lang.Exception: Some exception."},{"module":"java.lang","stacktrace":{"frames":[{"native":false,"filename":"ZygoteInit.java","function":"main","in_app":false,"lineno":616,"module":"com.android.internal.os.ZygoteInit"},{"native":false,"filename":"ZygoteInit.java","function":"run","in_app":false,"lineno":726,"module":"com.android.internal.os.ZygoteInit$MethodAndArgsCaller"},{"native":true,"filename":"Method.java","function":"invoke","in_app":false,"module":"java.lang.reflect.Method"},{"native":false,"filename":"ActivityThread.java","function":"main","in_app":false,"lineno":5417,"module":"android.app.ActivityThread"},{"native":false,"filename":"Looper.java","function":"loop","in_app":false,"lineno":148,"module":"android.os.Looper"},{"native":false,"filename":"Handler.java","function":"dispatchMessage","in_app":false,"lineno":95,"module":"android.os.Handler"},{"native":false,"filename":"Handler.java","function":"handleCallback","in_app":false,"lineno":739,"module":"android.os.Handler"},{"native":false,"filename":"View.java","function":"run","in_app":false,"lineno":21147,"module":"android.view.View$PerformClick"},{"native":false,"filename":"View.java","function":"performClick","in_app":false,"lineno":5198,"module":"android.view.View"},{"native":false,"filename":"lambda","function":"onClick","
```

Closes #298, #296. Thanks to marandaneto for the initial implementation.

sentry-core/src/main/java/io/sentry/core/transport/StdoutTransport.java

@@ -0,0 +1,30 @@
+package io.sentry.core.transport;
+
+import io.sentry.core.ISerializer;
+import io.sentry.core.SentryEvent;
+import java.io.IOException;
+import java.io.OutputStreamWriter;
+import java.io.PrintWriter;
+import java.io.Writer;
+import java.nio.charset.Charset;
+
+public final class StdoutTransport implements ITransport {
+  private final ISerializer serializer;
+
+  public StdoutTransport(final ISerializer serializer) {
+    this.serializer = serializer;
+  }
+
+  @Override
+  public TransportResult send(SentryEvent event) throws IOException {
+    Writer outputStreamWriter = new OutputStreamWriter(System.out, Charset.defaultCharset());
+    PrintWriter printWriter = new PrintWriter(outputStreamWriter);
+
+    serializer.serialize(event, printWriter);
+
+    return TransportResult.success();
+  }
+
+  @Override
+  public void close() {}
+}

sentry-core/src/test/java/io/sentry/core/transport/StdoutTransportTest.kt

@@ -0,0 +1,37 @@
+package io.sentry.core.transport
+
+import com.nhaarman.mockitokotlin2.any
+import com.nhaarman.mockitokotlin2.eq
+import com.nhaarman.mockitokotlin2.mock
+import com.nhaarman.mockitokotlin2.verify
+import io.sentry.core.ISerializer
+import io.sentry.core.SentryEvent
+import io.sentry.core.SentryOptions
+import org.junit.Test
+import kotlin.test.assertTrue
+
+class StdoutTransportTest {
+    private class Fixture {
+        val serializer = mock<ISerializer>()
+
+        fun getSUT(): ITransport {
+            val options = SentryOptions()
+            options.setSerializer(serializer)
+
+            return StdoutTransport(serializer)
+        }
+    }
+
+    private val fixture = Fixture()
+
+    @Test
+    fun `test serializes event`() {
+        val transport = fixture.getSUT()
+        val event = SentryEvent()
+
+        val result = transport.send(event)
+
+        verify(fixture.serializer).serialize(eq(event), any())
+        assertTrue(result.isSuccess)
+    }
+}