Add return constants package, and common message sender functions

Trying to resolve as much as possible ``gometalinter`` issues.

lib/sender/exported.go

@@ -0,0 +1,28 @@
+// i2_bot – Instinct PokememBro Bot
+// Copyright (c) 2018 Vladimir "fat0troll" Hodakov
+
+package sender
+
+import (
+	"source.wtfteam.pro/i2_bot/i2_bot/lib/appcontext"
+	"source.wtfteam.pro/i2_bot/i2_bot/lib/sender/senderinterface"
+)
+
+var (
+	c *appcontext.Context
+)
+
+// Sender is a function-handling struct for sender
+type Sender struct{}
+
+// New is a appcontext initialization function
+func New(ac *appcontext.Context) {
+	c = ac
+	s := &Sender{}
+	c.RegisterSenderInterface(senderinterface.SenderInterface(s))
+}
+
+// Init is an initialization function for sender
+func (s *Sender) Init() {
+	c.Log.Info("Initializing Sender...")
+}