Input: convert gameport programming documentation into ReST format

This file require minimum adjustments to be a valid ReST.  Do it, in order
to be able to parse it with Sphinx.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>