implements #409: added strict monotonicity flag for hierarchical segmentation metrics

[tomxi]

This PR implements issue #409.
It adds strict monotonicity flag for hierarchical segmentation metrics.
Also added new tests for coverage.

Soliciting feedback.

[tomxi]

Besides the _meet function and l-measure mentioned in #409, this PR also gave t-measure and the _lca function the same treatment.

I also fixed up the doc string for _meet as it was copied over from _lca and needed a minor updates.

[tomxi]

Hmm.. CI checks are failing after the unit tests, at the upload coverage to Codecov step...

Can I get some help/guidance on how to resolve this?

[bmcfee]

Can I get some help/guidance on how to resolve this?

TLDR you can't. We went round on this with the codecov devs a couple weeks ago, and couldn't really resolve it but my suspicion is that something screwy happened with permissioning when we migrated to an organization repo. It works for PRs originating from the main repo, but not from forks.

We could make it so that failing coverage will not break the status, but that's not a great solution IMO.