Many improvements

Thanks for your plugin! I made some pretty substantial improvements, including dividing settings into more readable dicts and allowing for commands based on file name, folder, extension, or root name and including variables (like project folder, filename, etc.) in the command. 

The example in the settings is for Less.js from Twitter Bootstrap, as whenever you save a file with the ".less" extension, it automatically rebuilds bootstrap.css from bootstrap.less. It's already saved me many times bouncing back to the terminal.