Add a custom stylesheet to the documentation.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
doc: css changes for gnome web

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
doc: couple of minor documentation fixes

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>