Added ToPoint3d methods

made EndVertex public
changed SplitEdge to use midpoint
Revert "changed SplitEdge to use midpoint"

This reverts commit 0dd27d5b5d63a76ccfad2f3c4fcd68ad6be2b6e7.
Update TriangleSplitEdge parameters
Merge branch 'mesh-ops' of https://github.com/Dan-Piker/Plankton into mesh-ops
Add new halfedge circulators and organise methods in collections

* traverse from a specific halfedge, either:
    * around its start vertex, or
    * around its adjacent face
* organise methods into: traversals, adj queries, euler and helpers
* mark old circulators as obsolete, need to go through and call new ones instead