Set HTTP client via option. Update readme, Makefile, go.sum

Signed-off-by: Vartan Benohanian <vartanbeno@gmail.com>

reddit/reddit-options.go

@@ -1,6 +1,8 @@
 package reddit
 
 import (
+	"errors"
+	"net/http"
 	"net/url"
 	"os"
 )
@@ -8,8 +10,18 @@ import (
 // Opt is a configuration option to initialize a client.
 type Opt func(*Client) error
 
+// WithHTTPClient sets the HTTP client which will be used to make requests.
+func WithHTTPClient(httpClient *http.Client) Opt {
+	return func(c *Client) error {
+		if httpClient == nil {
+			return errors.New("httpClient: cannot be nil")
+		}
+		c.client = httpClient
+		return nil
+	}
+}
+
 // FromEnv configures the client with values from environment variables.
-//
 // Supported environment variables:
 // GO_REDDIT_CLIENT_ID to set the client's id.
 // GO_REDDIT_CLIENT_SECRET to set the client's secret.
@@ -19,19 +31,15 @@ func FromEnv(c *Client) error {
 	if v := os.Getenv("GO_REDDIT_CLIENT_ID"); v != "" {
 		c.ID = v
 	}
-
 	if v := os.Getenv("GO_REDDIT_CLIENT_SECRET"); v != "" {
 		c.Secret = v
 	}
-
 	if v := os.Getenv("GO_REDDIT_CLIENT_USERNAME"); v != "" {
 		c.Username = v
 	}
-
 	if v := os.Getenv("GO_REDDIT_CLIENT_PASSWORD"); v != "" {
 		c.Password = v
 	}
-
 	return nil
 }
 
@@ -42,7 +50,6 @@ func WithBaseURL(u string) Opt {
 		if err != nil {
 			return err
 		}
-
 		c.BaseURL = url
 		return nil
 	}
@@ -55,7 +62,6 @@ func WithTokenURL(u string) Opt {
 		if err != nil {
 			return err
 		}
-
 		c.TokenURL = url
 		return nil
 	}