Adding decorators for parsing commands.

[mikegrima]

• Significant refactor
• Adds a lot of niceties and removes need for copypasta

[mikegrima]

Added an @auth() decorator which is to be used in conjunction with the @hubcommander_command() decorator.

This should mostly be stable, but I would like to convert some GitHub commands over before merging.

[mikegrima]

Added some more decorators in, such as:

• @github_user_exists
• @repo_must_exist

and currently converting all of the GitHub commands over to the new decorated model.

The new decorators also have the ability of specifying if an argument should be all lowercase, uppercase, or case-sensitive.

[mikegrima]

Added a new decorator @branch_must_exist

[mikegrima]

Updated the documentation. Will need to do some more testing before merging.