Browser distribution should be wrapped in an IIFE

[benquarmby]

Firstly, the browser distribution of mocha-given (/browser/mocha-given.js) is very much appreciated!

However, the compiled JavaScript currently pollutes the browser's global scope with all of the module's variables. I believe that compiling CoffeeScript without the --bare option should fix that.

[jasonkarns]

can we get this resolved? will a PR get this moving?