Make docbook valid

Fixed invalid docbook syntax especially the "id" attribute of the
elements where the attribute was with more than one word combined the
words with '_" so they will be easy to read.

Add declaration when necessary so document is valid by itself

Fix all documents so they are docbook valid.

Use <section> in favor of all other sect variants, since this makes
moving the sections easier

Signed-off-by: madanyang <toganm@opensuse.org>