doc-rst: customize RTD theme, drop padding of inline literal

Remove the distracting (left/right) padding of inline literals. (HTML
<code>). Requested and discussed in [1].

[1] http://www.spinics.net/lists/linux-media/msg103991.html



Signed-off-by: Markus Heiser <markus.heiser@darmarIT.de>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>