This PR adds two new arguments to the list-caps command.

Capability Origin

Fixes: #99

The first is the --origin= attribute which allows you to specify:

• all (default) Returns all capabilities
• role returns only the capabilities inherited because a user has a role
• user returns only the capabilities directly assigned to a user (ex: `wp user add-cap bob newcap)

Exclude Role Names

The second is a flag --exclude-role-names that removes a capability from the returned list if it matches the name of a role. For example, if a user has the contributor role, the value 'contributor' would not be returned if --exclude-role-names was specified, but the individual capabilities that role included, like read would be.