Add simple plugin for chruby ruby version manager

plugins/chruby/chruby.plugin.zsh

+#
+# INSTRUCTIONS
+#
+#  With either a manual or brew installed chruby things should just work.
+#
+#  If you'd prefer to specify an explicit path to load chruby from
+#  you can set variables like so:
+#
+#    zstyle :omz:plugins:chruby path /local/path/to/chruby.sh
+#    zstyle :omz:plugins:chruby auto /local/path/to/auto.sh
+# 
+# TODO
+#  - autodetermine correct source path on non OS X systems
+#  - completion if ruby-install exists
+
+# rvm and rbenv plugins also provide this alias
+alias rubies='chruby'
+
+local _chruby_path
+local _chruby_auto
+
+_homebrew-installed() {
+    whence brew &> /dev/null
+}
+
+_chruby-from-homebrew-installed() {
+    brew --prefix chruby &> /dev/null
+}
+
+_ruby-build_installed() {
+    whence ruby-build &> /dev/null
+}
+
+_ruby-install-installed() {
+    whence ruby-install &> /dev/null
+}
+
+# Simple definition completer for ruby-build
+if _ruby-build_installed; then
+    _ruby-build() { compadd $(ruby-build --definitions) }
+    compdef _ruby-build ruby-build
+fi
+
+_source_from_omz_settings() {
+    zstyle -s :omz:plugins:chruby path _chruby_path
+    zstyle -s :omz:plugins:chruby auto _chruby_auto
+
+    if _chruby_path && [[ -r _chruby_path ]]; then
+        source ${_chruby_path}
+    fi
+
+    if _chruby_auto && [[ -r _chruby_auto ]]; then
+        source ${_chruby_auto}
+    fi
+}
+
+_chruby_dirs() {
+    chrubydirs=($HOME/.rubies/ $PREFIX/opt/rubies)
+    for dir in chrubydirs; do
+        if [[ -d $dir ]]; then
+            RUBIES+=$dir
+        fi
+    done
+}
+
+if _homebrew-installed && _chruby-from-homebrew-installed ; then
+    source $(brew --prefix chruby)/share/chruby/chruby.sh
+    source $(brew --prefix chruby)/share/chruby/auto.sh
+    _chruby_dirs
+elif [[ -r "/usr/local/share/chruby/chruby.sh" ]] ; then
+    source /usr/local/share/chruby/chruby.sh
+    source /usr/local/share/chruby/auto.sh
+    _chruby_dirs
+else
+    _source_from_omz_settings
+    _chruby_dirs
+fi
+
+function ensure_chruby() {
+    $(whence chruby)
+}
+
+function current_ruby() {
+    local _ruby
+    _ruby="$(chruby |grep \* |tr -d '* ')"
+    if [[ $(chruby |grep -c \*) -eq 1 ]]; then
+        echo ${_ruby}
+    else
+        echo "system"
+    fi
+}
+
+function chruby_prompt_info() {
+    echo "$(current_ruby)"
+}
+
+# complete on installed rubies
+_chruby() { compadd $(chruby | tr -d '* ') }
+compdef _chruby chruby