Use some ~abstraction~ and move more stuff around, much to everyone's misery

[redshadowhero]

Should address #40

I also took the opportunity to move xivdpscalc.pps.pps into just xivdpscalc.pps, since that's cleaner and makes more sense:

from xivdpscalc.pps.pps import HealerPps

doesn't feel as good as

from xivdpscalc.pps import HealerPps