Ability to pass a client to the bot

Changed every instance of a DefaultClient to a Client stored in the bot.

bot.go

@@ -1,19 +1,27 @@
 // Package tgbotapi has bindings for interacting with the Telegram Bot API.
 package tgbotapi
 
+import "net/http"
+
 // BotAPI has methods for interacting with all of Telegram's Bot API endpoints.
 type BotAPI struct {
 	Token   string      `json:"token"`
 	Debug   bool        `json:"debug"`
 	Self    User        `json:"-"`
 	Updates chan Update `json:"-"`
+	Client  http.Client `json:"-"`
 }
 
 // NewBotAPI creates a new BotAPI instance.
 // Requires a token, provided by @BotFather on Telegram
-func NewBotAPI(token string) (*BotAPI, error) {
+func NewBotAPI(token string, client http.Client) (*BotAPI, error) {
+	if client == nil {
+		client = &http.Client{}
+	}
+
 	bot := &BotAPI{
-		Token: token,
+		Token:  token,
+		Client: client,
 	}
 
 	self, err := bot.GetMe()