Add basic implementation of pointsinside based on Rvcg

* Rvcg::vcgClost has a signed distance function but the result
  only seems to make sense for whole brain surfaces
* but not neuropil surfaces
* assume this has to do with how they are closed
Update to match up with fixed surface normals
Add test for pointsinside
minor doc fix - prune.dotprops has moved to nat
Merge branch 'feature/points-in-surf'

* feature/points-in-surf:
  minor doc fix - prune.dotprops has moved to nat
  Add test for pointsinside
  Update to match up with fixed surface normals
  Add basic implementation of pointsinside based on Rvcg