2.0.0 RC1

CHANGELOG:

• support working on forks by introducing --upstream on command create.
• add remotes when using checkout on requests from forks.
• remove obsolete remotes on command clean.
• change default behavior for command checkout and introduce --no-branch.
• fix displaying comments for commands list and show.
• fix keyboard input when asking for a branch name.
• boost performance by using threads.
• use octokit 2.0.
• lots of internal refactoring.