added some category explanations
added missing class definitions
Merge pull request #3 from mjansing/explanations

Explanations
cleanup
adding CORS
MD test
rollback MD test
using ugly unicode quotation marks to hack around MD stupidity
using plurals for the lists
changing status of "HTML Canvas 2D Context" from WD to CR
adding spec counts per category
moving "Ambient Light Events" and "Proximity Events" from WD to CR
moving XSLTs to XSLT/