Use an optional dependency on flint to speed up #526
Description
According to the SymPy mailing list, there are a series of PRs to use FLINT to speed things up.
FLINT will need to remain an optional dependency as it's LGPL licensed, and we might not want to force that on users of GAlgebra.
Similar considerations for GiNaC, but no known work around that on SymPy.
This issue might supersede #37 .