Add client side opt in for image inlining

Fixes #79.
Do we really want this to be a global variable?

Generally speaking, if you're using an [IIFE](http://benalman.com/news/2010/11/immediately-invoked-function-expression/) as module wrapper, the entire code should reside within that wrapper. If you want to expose something to the outside, you could use the [revealing module pattern](http://christianheilmann.com/2007/08/22/again-with-the-module-pattern-reveal-something-to-the-world/), for example.