doc-rst: customize RTD theme, captions & inline literal

The layout of (table) captions in the RTD theme is a bit ugly and the
bordered, red colored of inline literals is a bit to gaudy. The
requirements has been discussed in the ML [1].

captions:

  - captions should have 100% (not 85%) font size
  - hide the permalink symbol as long as link is not hovered

inline literal:

  - drop the borderbox and red color

[1] http://article.gmane.org/gmane.linux.drivers.video-input-infrastructure/101099



Signed-off-by: Markus Heiser <markus.heiser@darmarIT.de>