feat: add support for setting URL parameters on client requests

Several NS1 API endpoints allow setting URL parameters to alter the
behavior of the endpoint. For instance, a `limit` parameter can be set
on the `/account/activity` endpoint to control how many events are
returned in the response. This would be useful in ns1#233.

This commit adds support for URL parameters by adding a new struct
`Param` to the `rest` package, and updating `rest.client.Do()` and
`rest.client.DoWithPagination()` to accept a variable amount of params.
In order for higher level services based off of the common service to
set url params, they will need to pass them through when invoking the
client's `Do()` method, like so:

```golang
resp, err := s.client.Do(req, &al, params...)
```

mockns1/testcase.go

@@ -8,6 +8,7 @@ import (
 	"strings"
 
 	"github.com/stretchr/testify/assert"
+	api "gopkg.in/ns1/ns1-go.v2/rest"
 )
 
 type testCase struct {
@@ -29,13 +30,19 @@ func (s *Service) AddTestCase(
 	method, uri string, returnStatus int,
 	requestHeaders, responseHeaders http.Header,
 	requestBody, responseBody interface{},
+	params ...api.Param,
 ) error {
 	s.stopTimer()
 	defer s.startTimer()
 
 	if !strings.HasPrefix(uri, "/v1/") {
 		uri = "/v1/" + uri
 	}
+
+	for _, p := range params {
+		uri = fmt.Sprintf("%s?%s=%s", uri, p.Key, p.Value)
+	}
+
 	uri = strings.Replace(uri, "//", "/", -1)
 
 	tc := &testCase{

rest/client.go

@@ -185,10 +185,20 @@ func SetDDIAPI() func(*Client) {
 	return func(c *Client) { c.DDI = true }
 }
 
+type Param struct {
+	Key, Value string
+}
+
 // Do satisfies the Doer interface. resp will be nil if a non-HTTP error
 // occurs, otherwise it is available for inspection when the error reflects a
 // non-2XX response.
-func (c Client) Do(req *http.Request, v interface{}) (*http.Response, error) {
+func (c Client) Do(req *http.Request, v interface{}, params ...Param) (*http.Response, error) {
+	q := req.URL.Query()
+	for _, p := range params {
+		q.Set(p.Key, p.Value)
+	}
+	req.URL.RawQuery = q.Encode()
+
 	resp, err := c.httpClient.Do(req)
 	if err != nil {
 		return nil, err
@@ -228,8 +238,8 @@ type NextFunc func(v *interface{}, uri string) (*http.Response, error)
 // Response is from the last URI visited - either the last page, or one that
 // responded with a non-2XX status. If a non-HTTP error occurs, resp will be
 // nil.
-func (c Client) DoWithPagination(req *http.Request, v interface{}, f NextFunc) (*http.Response, error) {
-	resp, err := c.Do(req, v)
+func (c Client) DoWithPagination(req *http.Request, v interface{}, f NextFunc, params ...Param) (*http.Response, error) {
+	resp, err := c.Do(req, v, params...)
 	if err != nil {
 		return resp, err
 	}