[css3-flexbox] ED updated: algorithms and 'flex' property

I have updated the spec with yesterday's feedback on algorithms and changed "flex()" to 'flex' as we agreed at F2F.

The only significant change left to do is finalize what auto margins do and put it in the spec. Otherwise, the spec should be ready for review (while editors add examples and clean up text).

Tab - do the changes look OK? Agree on my assessment of spec status?