[why]
We want to patch some fonts with different font-patcher options.
[how]
Use the config.cfg file that each source font can have to specify one
arbitrary option to the font-patcher calls.
[note]
This is partially commit 9e2bc9a26 from #723.
Signed-off-by: Fini Jastrow <ulf.fini.jastrow@desy.de>