doc/default.css + doc/t2h.init: New styles

The main motive of this commit is to make the offline copy of the HTML doc as
pretty as the online (ffmpeg.org) one. This also introduced new styles for
<h2> to <h4>.

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
MAINTAINERS: add Communication section

Add Twitter with myself (Lou Logan) as maintainer.

Add Google+ with Paul B Mahol, Michael Niedermayer, and Alexander
Strasser as maintainers.

Move website and mailinglists from Miscellaneous Areas to
Communication.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>