build-sys: add parse-date.y

build-sys: add parse-date.y

* add lib/parse-date.y to build system
* add necessary autotools stuff to generate .c on the fly
  (autotools are smart enough to add generated file to tarball)
* check for bison version by ./autogen.sh
* add non-wanted junk to .gitignore

With some modification by J William Piggott with regard to
moving the parse-date API into timeutils.h

Signed-off-by: J William Piggott <elseifthen@gmx.com>