add: rbenv plugin

plugins/rbenv/rbenv.plugin.zsh

@@ -0,0 +1,37 @@
+rbenvdir=$HOME/.rbenv/bin
+if [ -d $rbenvdir ] ; then
+  export PATH=$rbenvdir:$PATH
+  eval "$(rbenv init -)"
+
+  alias rubies="rbenv versions"
+  alias gemsets="rbenv gemset list"
+
+  function current_ruby() {
+    echo "$(rbenv version | cut -f1 -d ' ')"
+  }
+
+  function current_gemset() {
+    echo "$(rbenv gemset active 2&>/dev/null | grep -v 'no active gemsets')"
+  }
+
+  function gems {
+    local rbenv_path=$(rbenv prefix)
+    gem list $@ | sed \
+      -Ee "s/\([0-9\.]+( .+)?\)/$fg[blue]&$reset_color/g" \
+      -Ee "s|$(echo $rbenv_path)|$fg[magenta]\$rbenv_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() {
+    if [[ -n $(current_gemset) ]] ; then
+      echo "$(current_ruby)@$(current_gemset)"
+    else
+      echo "$(current_ruby)"
+    fi
+  }
+else
+  alias rubies='ruby -v'
+  function gemsets() { echo 'not supported' }
+  function rbenv_prompt_info() { echo "system: $(ruby -v | cut -f-2 -d ' ')" }
+fi