Yaml to html

Usage: OpenRA.Utility --stats MOD [output directory]

This adds a utility that converts the yaml files to html. This is intended to provide a website where people can see the current stats for units, etc. in release, and in bleed (to see what is coming).

A very simple example .css file is included in html/

I'm making this PR because the utility works, but also to get some feedback into features I should add and how I should do things.