Vim and Ruby enhancements

New vim plugins:
- vim-endwise
- vim-projectionist
- vim-rake
- vim-ruby
- tagbar
- ctrlp.vim

Updated .vimrc with <F6> shortcut for tagbar

New homebrew dependencies:
- ctags
- rbenv-default-gems
- rbenv-ctags
- rbenv-gem-rehash

Also set $RBENV_ROOT ENV var.  It's needed by rbenv-default-gems.