This gets everything but the actual shadow map bindings working: the
validation layers don't like my type punning (which may well be the
right thing) and specialization constants don't help (yet, anyway) but I
want to get things into git.
Samplers have no direct relation to render passes or pipelines, so
should not necessarily be in the same config file. This makes all the
old config files obsolete, and quite a bit of support code in vkparse.c.
