(WIP) Loader - incorporate pathogen encoding logic in a separate module under loader.

This is a follow up to https://github.com/yui/yui3/pull/1813. 
I created this pull request specifically for feedback as to the direction that needs to be taken.

@caridy
@juandopazo
@ekashida
oh, I see, it is suppose to be a config that you pass in to bootstrap using a module different than `loader`. there might be some troubles with this because I recall a couple of implementations trying to mess up with `loader` module name, but overall seems like a simple config. Let's pock around to see if there is any other better option, if not, we can proceed with this one. /cc @ericf