Move maths types into math/ dir.
Update .gitignore.
Add snow/logging/, move config into config.hh

snow-common.hh now includes headers in snow-common that aren't dependent
on outside libraries/sources that wouldn't typically be available.
Add lb_push_value/to_value specializations for prims

So, now there's int, long, size_t, float, and double.
Update header guards with new prefix.