Deprecation: Client#addCommandDir, Client#addCommandFile, Client#reloadCommands

[eritbh]

The Client methods addCommandDir, addCommandFile, and reloadCommands were all deprecated in #29, when the EventListener class was added. These functions now serve only as aliases for addDir, addFile, and reloadFiles respectively, which means that despite their names, they are not actually limited to working on commands, but impact both commands and event listeners loaded from files. These methods can be directly replaced in consumer code.

addCommandDir, addCommandFile, and reloadCommands will be removed in the 3.0.0 release (#94).