Support indented syntax *.sass files, compile by default without preferences

This is a biggie!

* Updates node-sass to 0.9.3 https://github.com/sass/node-sass/releases/tag/v0.9.3 with a small monkey patch to work around a `SIGBUS` error https://github.com/sass/node-sass/pull/366. A quick scrub of the releases between 0.8.4 and 0.9.3 shows a few highlights
    * Update libsass https://github.com/sass/libsass to 2.0 ( .sass syntax and BEM-selector support), then 2.1.0-beta
    * To be clear, this enables the indented SASS syntax and fixes #5 without integrating the Ruby compiler (see #3)
* Compiles any non-partial sass/scss files by default (files starting with an underscore e.g. `_myimport.sass`) 
* Use git SHA in grunt build when creating .zip file, e.g. `jasonsanjose.brackets-sass.0.4.0+sha.2948e5c.zip`
* Run `node-sass` as a forked child_process to guard against fatal errors