doc-rst: add parse-headers.pl script

This script parses a header file and converts it into a
parsed-literal block, creating references for ioctls,
defines, typedefs, enums and structs.

It also allow an external file to modify the rules, in
order to fix the expressions.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>