Documentation: core-api: add generic parser docbook

Documentation: core-api: add generic parser docbook

Add the simple generic parser to the core-api docbook.
It can be used for parsing all sorts of options throughout the kernel.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Eric Biggers <ebiggers@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20241120060711.159783-1-rdunlap@infradead.org