add: rbenv plugin

plugins/rbenv/rbenv.plugin.zsh

@@ -0,0 +1,44 @@
+FOUND_RBENV=0
+for rbenvdir in "$HOME/.rbenv" "/usr/local/rbenv" "/opt/rbenv" ; do
+  if [ -d $rbenvdir/bin -a $FOUND_RBENV -eq 0 ] ; then
+    FOUND_RBENV=1
+    export RBENV_ROOT=$rbenvdir
+    export PATH=${rbenvdir}/bin:$PATH
+    eval "$(rbenv init -)"
+
+    alias rubies="rbenv versions"
+    alias gemsets="rbenv gemset list"
+
+    function current_ruby() {
+      echo "$(rbenv version-name)"
+    }
+
+    function current_gemset() {
+      echo "$(rbenv gemset active 2&>/dev/null | sed -e ":a" -e '$ s/\n/+/gp;N;b a') | head -n1"
+    }
+
+    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
+    }
+  fi
+done
+unset rbenvdir
+
+if [ $FOUND_RBENV -eq 0 ] ; then
+  alias rubies='ruby -v'
+  function gemsets() { echo 'not supported' }
+  function rbenv_prompt_info() { echo "system: $(ruby -v | cut -f-2 -d ' ')" }
+fi