context: implement Bot function

context.go

@@ -14,6 +14,9 @@ type HandlerFunc func(Context) error
 // Context represents a context of the current event. It stores data
 // depending on its type, whether it's a message, callback or whatever.
 type Context interface {
+	// Bot returns the bot instance.
+	Bot() *Bot
+
 	// Message returns stored message if such presented.
 	Message() *Message
 
@@ -159,6 +162,10 @@ type nativeContext struct {
 	store map[string]interface{}
 }
 
+func (c *nativeContext) Bot() *Bot {
+	return c.b
+}
+
 func (c *nativeContext) Message() *Message {
 	switch {
 	case c.message != nil: