Rework mask

[rowanwins]

This PR reworks the mask module to be much simpler.

It's a bit slower on some of the tests (like surprisingly so) although I haven't quite dug into why deeply, it's most likely something to do with the union operation being called when it probably doesn't need to be.

This work was originally included in my v7 branch.

Resolves #1944
Resolves #1917
Resolves #2054
Resolves #1454

Before

basic x 2,599,035 ops/sec ±0.45% (93 runs sampled)
mask-outside x 2,445,808 ops/sec ±1.50% (86 runs sampled)
multi-polygon x 5,336 ops/sec ±1.80% (84 runs sampled)
overlapping x 15,862 ops/sec ±0.98% (93 runs sampled)

After

basic x 4,627 ops/sec ±25.23% (21 runs sampled)
mask-outside x 3,892 ops/sec ±34.80% (15 runs sampled)
multi-polygon x 5,837 ops/sec ±3.03% (91 runs sampled)
overlapping x 22,326 ops/sec ±1.34% (90 runs sampled)

[mfedderly]

Can you rework this PR to remove the commits from the release? its hard to examine the diff. Thanks!