Joins ruby prompt files and adds ruby_prompt_info.

lib/chruby.zsh

-# using the chruby plugin will override this with a real implementation
-function chruby_prompt_info() {
-  return 1
-}

lib/rbenv.zsh

-# using the rbenv plugin will override this with a real implementation
-function rbenv_prompt_info() {
-  return 1
-}

lib/rvm.zsh → lib/ruby_prompts.zsh

-# get the name of the ruby version
+# get the name of the rvm ruby version
 function rvm_prompt_info() {
   [ -f $HOME/.rvm/bin/rvm-prompt ] || return 1
   local rvm_prompt
@@ -6,3 +6,17 @@ function rvm_prompt_info() {
   [[ "${rvm_prompt}x" == "x" ]] && return 1
   echo "${ZSH_THEME_RVM_PROMPT_PREFIX:=(}${rvm_prompt}${ZSH_THEME_RVM_PROMPT_SUFFIX:=)}"
 }
+
+# using the rbenv plugin will override this with a real implementation
+function rbenv_prompt_info() {
+  return 1
+}
+
+# using the chruby plugin will override this with a real implementation
+function chruby_prompt_info() {
+  return 1
+}
+
+function ruby_prompt_info() {
+  echo $(rvm_prompt_info || rbenv_prompt_info || chruby_prompt_info)
+}