Create discord package and connect/disconnect handlers

This change moves the discord session singleton to the internal/discord
package, and implements basic Connect/Disconnect handlers.

internal/discord/handlers.go

@@ -0,0 +1,21 @@
+package discord
+
+import (
+	"github.com/bwmarrin/discordgo"
+	"gitlab.com/whom/bingobot/internal/logging"
+)
+
+func addHandlers() {
+	session.s.AddHandler(handleConnect)
+	session.s.AddHandler(handleDisconnect)
+}
+
+func handleConnect(s *discordgo.Session, e *discordgo.Connect) {
+	session.connected = true
+	logging.Info("discord session connected")
+}
+
+func handleDisconnect(s *discordgo.Session, e *discordgo.Disconnect) {
+	session.connected = false
+	logging.Info("discord session disconnected")
+}