v401 Update

[seanhandley]

Migrate to v4.0.1

There are many breaking changes: https://github.com/uber/h3/releases/tag/v4.0.0-rc1

Migration guide: https://h3geo.org/docs/next/library/migration-3.x/functions/

Headers: https://github.com/uber/h3/blob/v4.0.0-rc1/src/h3lib/include/h3api.h.in

[kbaribeau]

Just on the off chance someone else is interested in the v4 upgrade: I've pushed some changes to this branch up to my fork

It's still far from complete, but I've made some progress. The docs still need lots of attention.

But, most specs are now passing (there are still failures in hierarchy_spec.rb, and unidirectional_edges_spec.rb will segfault if its run).

[seanhandley]

Replaced by #123