Docs,  opt-out keys

If the key value is not nonzero, a secret __ key is provided instead
rationalized event metadata

to make sure Event and MayaEvent don't diverge
Cleanup, rename, added horizontal list

List classes are now named "List"
They come with inherent scroll bars
changed 'gui' to 'sender'

events include 'sender' in their data now
Horizontal checks for controls in layout()

fixing issue with 0-length control lists
Reflects latest syntax