doc-rst: parse-headers: fix multiline typedef handler

The typedef handler should do two things to be generic:
  1) parse typedef enums;
  2) accept both possible syntaxes:
	 typedef struct foo { .. } foo_t;
	 typedef struct { .. } foo_t;

Unfortunately, this is needed to parse some legacy DVB
files, like dvb/audio.h.

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