added 'split' pipe that was missing, and fixed a bug I just fixed on Markup.js too

For some reason the 'split' pipe was missing from the core pipes, so I added it.

I also contributed a fix for broken loops when using pipes to convert variables into arrays (I'm currently relying on this for a bunch of custom pipes and using 'split' as well in a project)

Same patch for Markup.js here : https://github.com/adammark/Markup.js/pull/19