standardize plugins, update metadata

add about-plugin metadata
chmod -x plugins
cleanup filenames to standardize on x.plugin.bash format
only plugin files intended to be executable from the command line should
contain a shebang line, and should be a+x.

plugins/available/ruby.plugin.bash

@@ -1,4 +1,10 @@
-#!/usr/bin/env bash
+cite about-plugin
+about-plugin 'adds "remove_gem" function'
+
 function remove_gem {
+  about 'removes installed gem'
+  param '1: installed gem name'
+  group ruby
+
   gem list | grep $1 | awk '{ print $1; }' | xargs sudo gem uninstall
 }