List discrepencies from pure tomdoc

This PR:

* Trashes the bogus Changelog
* Cleans up the CONTRIBUTING guidelines a bit
* Updates the README to provide more information on TomDoc syntax, and, specifically, deviations from TomDoc syntax

/cc @kevinsawicki Can I get a :+1: for the deviations? I think I got them all.
/cc @mojombo for info