WIP Add more traits function for better API design

[jonaselan]

I believe it would be interesting for the project if there were more auxiliary functions, such as user.hasPermissionTo() or user.hasAllPermissions(). In this pull request I made just one example, if they find it interesting, I can create more.

Note: I had problems with coveralls (which can be seen on travis). This problem is already known, but I did not go too far to solve it.