Build the documentation

Signed-off-by: Thomas Braun <thomas.braun@byte-physics.de>
Add packages required for make doc in mingw32-git

The directly required packages are:
msys-asciidoc
msys-libxslt
msys-xmlto

And these packages depend on
msys-docbook
msys-getopt
msys-libxml2 (I could not get the stock package to work)

Currently the package msys-docbook requires manual invocation of
docbook-post-install.sh after installation.

Signed-off-by: Thomas Braun <thomas.braun@byte-physics.de>
Add msys-libffi and msys-python

Signed-off-by: Thomas Braun <thomas.braun@byte-physics.de>