Implement the command parser

Right now this just supports help and version, but will be getting new commands
shortly.

config/bridge.go

@@ -8,6 +8,8 @@ import (
 type bridge struct {
 	UsernameTemplate string `yaml:"username_template"`
 
+	CommandPrefix string `yaml:"command_prefix"`
+
 	ManagementRoomText managementRoomText `yaml:"management_root_text"`
 
 	PortalMessageBuffer int `yaml:"portal_message_buffer"`
@@ -31,6 +33,10 @@ func (b *bridge) validate() error {
 		return err
 	}
 
+	if b.CommandPrefix == "" {
+		b.CommandPrefix = "!dis"
+	}
+
 	if err := b.ManagementRoomText.validate(); err != nil {
 		return err
 	}