Adapt NEWS.rst to follow Twisted's style more closely

So this is my stab at it.

A couple of notes:

- I have replaced * by - because that’s what Twisted does in it’s NEWS file.  RST doesn’t care, so I can revert it if desired.
- I have slightly reordered the sections, again inspired by Twisted’s way.
- I have re-written the entries in intending accordance with http://twistedmatrix.com/trac/wiki/ReviewProcess#Newsfiles so please double-check both conformity and spelling/grammar.
- I have no idea what the point of “Fix deprecated exception error” is.

I can see the :ship: on the horizon.