New Features

* Add global `quiet` option which silences all hook output except in the case
  of warning or error

Changes

* Official support for Rubinius has been dropped. It will probably still work
  for most use cases, but parallelized hook runs may be problematic. If someone
  from the community is willing to step up to support it, we'll gladly add it
  back
* Change `overcommit` CLI to automatically run within a Bundler context if the
  `gemfile` option is specified. This mainly saves you from needing
  `bundle exec` when running `overcommit --run`

Bug Fixes

* Fix `AuthorName`/`AuthorEmail` pre-commit hooks to respect
  `GIT_AUTHOR_NAME`/`GIT_AUTHOR_EMAIL` environment variables, respectively
* Fix `JavaCheckstyle` pre-commit hook to ignore `[ERROR]` prefix when parsing
  output messages