Adding synchronous option for cases where the callback is called later than required (ie meteor)

Users of meteor are experiencing issues of not seeing their scss files rendered into css and included in the page. This appears to be due to a race condition where the callback is called after the page has been rendered.

For this I would like to add a synchronous option to node-sass, which defaults to false.

Relevant meteor issue here: https://github.com/meteor/meteor/issues/143

While there is no longer a sass meteorite add-on, My colleague is working on one now.