docs: Building with Makefile

[Björn JACKE]

On 2018-01-05 at 21:18 +0100 Andreas Schneider via samba-technical sent off:
> Why do you build with Makefile? Is the stuff in waf so bad?

simple Makefile with cleaned up dependencies just works best for me.
The waf doc build is a complex beast and I find it way more difficult to
oversee than the Makefile docs build. It starts with the point that there is no
dedicated waf make target for the docs as far as I can see.

Björn