added WCS-based pv extraction along with robust cube shape checkign
added vector-based PV extraction
bugfixes and cleanup
refactor endpoints -> x,y
some more refactoring?
notebook updated
Merge pull request #6 from astrofrog/refactor-geometry

Refactor geometry
Merge pull request #5 from keflavich/master

Add WCS-based PV extraction
Refactor using Paths