Bundler's binstubs DONE RIGHT

This is the ultimate solution to the `bundle exec` problem.

All gems in a Rails app/Ruby gem are automaticall installed into
`.bundle/gems` and binstubs into `.bundle/bin`.

If user cds into a directory with both `Gemfile.lock` and `.bundle`
directory present the `.bundle/bin` directory will be added to $PATH
and both $GEM_PATH and $GEM_HOME will be set correctly. If he then goes
to another directory, those changes will be reverted.
Change 'save' to <leader>w [vim]

Instead of previous '<leader>s'