Multi-branches

[kbond]

Currently, commands assume only one branch is maintained in a project: Github's default branch. For projects that maintain multiple branches (ie 1.x/2.x) this is a problem. Some general thoughts/ideas:

• add --branch= option to these commands
• error/ask if not set and multiple branches detected
• how to detect? probably if the source has multiple branches, ask
• will need to determine the proper --from [feature] add Version::matches() #18 might help