Refactor output implementation

[edwardstm]

Output should be handled in a more flexible way.

[gurnben]

I have an idea for this, but didn't feel it needed to be implemented right away. For each item, we can define certain items that can be output, such as the name, owner, organization, number of commits, number of branches, etc. for a given repository. If we do a similar static print function for commits, we can take in a cutoff date or number and options to print the committee, the commit message, the date/time, etc.

This is just an idea of course. There's probably a better implementation out there, I just originally went with the solution that allowed our class to abstract the interaction with github library objects from the user/client code!

[edwardstm]

Ref #27