Make sharing to community site optional (it's on by default)

For private/internal cookbook you may want to take advantage of the 
version bumping logic but choose to not share to the community sites for 
obvious reasons.
Make pushing to git remote optional (push will still happen by default)

You may want to delay pushing release commit/tag to configure remote.
Prompt for confirmation before releasing to community site

This prompt/question also properly respects the global `-y` or `--yes` 
knife options.
gitignore the `bin` directory generated by Bundler

This directory is generated by a `bundle install --binstubs`.
Merge branch 'support-no-push-or-share' of https://github.com/schisamo/knife-community
allow more than 30 lines in method
Adds changelog
minor version increment