add: rbenv plugin

plugins/rbenv/rbenv.plugin.zsh

@@ -0,0 +1,24 @@
+alias rubies='rbenv versions'
+alias gemsets='rbenv gemset list'
+
+# TODO: Make this usable w/o rbenv.
+function gems {
+  local current_ruby=`rbenv active | cut -f1 -d ' '`
+  local current_gemset=`rbenv gemset active | grep -v 'no active gemsets'`
+
+  gem list $@ | sed \
+    -Ee "s/\([0-9\.]+( .+)?\)/$fg[blue]&$reset_color/g" \
+    -Ee "s|$(echo $rvm_path)|$fg[magenta]\$rvm_path$reset_color|g" \
+    -Ee "s/$current_ruby@global/$fg[yellow]&$reset_color/g" \
+    -Ee "s/$current_ruby$current_gemset$/$fg[green]&$reset_color/g"
+}
+
+function rbenv_prompt_info() {
+  ruby_version=$(rbenv version | cut -f1 -d ' ') || return
+  gemset=$(rbenv gemset active 2&>/dev/null | grep -v 'no active gemsets')
+  if [[ -n $gemset ]] ; then
+    echo "${ruby_version}@${gemset}"
+  else
+    echo "${ruby_version}"
+  fi
+}