Added support for more WKT (grpc-ecosystem#816)

* Added support for more WKT

* Lint fix: added comments on exported functions

* Lint fix: added comments on exported functions

* Added end to end example to show support of StringValue in url option template

* updated more example protos; removed server and proxy for now

* Updated convert.go to fix float and other wkt

* brazel build fix

examples/pbwrappers/helloworld/BUILD.bazel

@@ -0,0 +1,39 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
+load("@io_bazel_rules_go//proto:def.bzl", "go_proto_library")
+
+proto_library(
+    name = "helloworld_proto",
+    srcs = ["helloworld.proto"],
+    visibility = ["//visibility:public"],
+    deps = [
+        "@com_google_protobuf//:wrappers_proto",
+        "@go_googleapis//google/api:annotations_proto",
+    ],
+)
+
+go_proto_library(
+    name = "helloworld_go_proto",
+    compilers = ["@io_bazel_rules_go//proto:go_grpc"],
+    importpath = "github.com/grpc-ecosystem/grpc-gateway/examples/pbwrappers/helloworld",
+    proto = ":helloworld_proto",
+    visibility = ["//visibility:public"],
+    deps = ["@go_googleapis//google/api:annotations_go_proto"],
+)
+
+go_library(
+    name = "go_default_library",
+    srcs = ["helloworld.pb.gw.go"],
+    embed = [":helloworld_go_proto"],
+    importpath = "github.com/grpc-ecosystem/grpc-gateway/examples/pbwrappers/helloworld",
+    visibility = ["//visibility:public"],
+    deps = [
+        "//runtime:go_default_library",
+        "//utilities:go_default_library",
+        "@com_github_golang_protobuf//proto:go_default_library",
+        "@org_golang_google_grpc//:go_default_library",
+        "@org_golang_google_grpc//codes:go_default_library",
+        "@org_golang_google_grpc//grpclog:go_default_library",
+        "@org_golang_google_grpc//status:go_default_library",
+        "@org_golang_x_net//context:go_default_library",
+    ],
+)