Nat
This PR implements support for `Nat` equalities and disequalities in the cutsat procedure.
simp +arith
This PR adds `simp +arith` for integers. It uses the new `grind` normalizer for linear integer arithmetic. We still need to implement support for dividing the coefficients by their GCD. It also fixes several bugs in the normalizer.
grind
lean-egg
Adapts, with permission, unit tests from `lean-egg` written by Marcus Rossel as regression tests for `grind`.
