Automatically generate ctags for rbenv Ruby stdlibs

I’ve got tags for my code base. I’ve got tags for my
gems. All I’m missing is tags for Ruby stdlib. Until now.

Installation

mkdir -p ~/.rbenv/plugins
git clone https://github.com/tpope/rbenv-ctags.git \
  ~/.rbenv/plugins/rbenv-ctags
rbenv ctags

You’ll also need Exuberant Ctags. With Homebrew, brew install ctags.
It is imperative that you make sure the correct ctags binary comes first in
your $PATH. Check ctags --version to verify.

Usage

Run rbenv ctags <version> to index the given version. If you are using
ruby-build as an rbenv plugin, this will happen automatically on install.

You need to configure your editor to look for tags files in the Ruby
$LOAD_PATH. If you’re using Vim, reasonably recent versions of vim-ruby
(and optionally rbenv.vim) take care of that for you.

You might also want to use rbenv-default-gems to automatically install
gem-ctags. Put it at the top of ~/.rbenv/default-gems so that it
indexes all gems underneath it.