exact: Port simplicity from sage to sympy

The simplicity script is now BSD licensed like the rest of core.
No more GPL'ed Sage controversy.
Merged
Merge branch 'master' of github.com:otherlab/core into sympy
Adds new exact predicates (rightwards,upwards) and float type support to BoxTree and its dependencies
Merged in changes from master
Merging in upstream
Merge branch 'master' of github.com:otherlab/core into sympy
WIP STASH COMMIT
Merge branch 'master' into sympy
HalfedgeMesh: Write and test a halfedge data structure
Merge branch 'master' into sympy
exact: Fix release mode warnings
HalfedgeMesh: Fix is_flip_safe

Thanks for Martin for catching this.  The unit test now verifies that
flips happen (tshirt?), so it will catch similar bugs in future.
math/numeric_limits: Accept anything convertible to a dtype
exact: Various cleanups

1. Comment tweaks here and there.
2. Factor SymbolicPoly out into a separate header.
3. Fix quantize to not divide by zero if all points are colocated.
exact: Resurrect a non-broken version of simplicity.py
exact/exact_tests: Test rightwards and upwards
exact: Inline trivial predicates
exact: Add an incircle test
exact: Add 1% slack around the quantized box for sentinel purposes

This will be useful for Delaunay.