(RFC) Convert optable.xml to YAML

The XML file is more verbose than it needs to be. YAML looks neater to me.

'make check' passes.

This is the script I used to generate optable.yml: https://gist.github.com/vegard/7474502

Consider this a proposal/request for comments, this is an old branch I had lying about, there could be issues I haven't run into yet.