Add a Pattern to Declare Global Variables

I had spent some time finding a way to do this while working with [Meteor.js](https://github.com/meteor/meteor), which needs global collection declarations.  Hope this might be useful for others.

References are [here](http://arcturo.github.io/library/coffeescript/02_syntax.html "Little Book on Coffeescript") and [here](http://raganwald.com/2013/07/27/Ive-always-been-mad.html "Ragan Wald's blog").