Add new convenience options like --no-branches, --stash, etc.

[mhagger]

All of the following can be accomplished using reference filtering (#75), but we could add new options to make them a tad more convenient (and these options would nicely complement --branches, --tags, and --remotes):

• --no-branches — equivalent to --exclude=refs/heads
• --no-tags — equivalent to --exclude=refs/tags
• --no-remotes — equivalent to --exclude=refs/remotes
• --notes / --no-notes — equivalent to --include=refs/notes / --exclude=refs/notes
• --stash / --no-stash — equivalent to --include=refs/stash / --exclude=refs/stash

[murayamajpeg]

git cat-file -p :