Add RubySyntaxGuard package

This package is a fork from https://github.com/edgar/RubyCheckOnSave . A month ago I forked it and changed default notification from opening ST console and put raw error from ruby interpreter to showing a popup window. The popup window includes a number of a line with error and a reason. After one month didn't got any feedback from author of original plugin, so I decided to publish it like a standalone plugin.