docs: kdoc_parser: Improve docstrings and comments

In preparation to document kernel-doc module, improve its
documentation.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <b6aabe25b45e9751885becd544a4db82dbe11ff2.1768838938.git.mchehab+huawei@kernel.org>

Author: mchehab