provide & and | operators for MinHash

[ctb]

In #1474 / #1392, we provide MinHash.intersection(...) which joins MinHash.merge(...) (equivalent to union).

At the time I couldn't figure out how to provide analogs to the set intersection and union operators, which are & and |. @luizirber pointed out that it's as simple as providing __and__ and __or__ on MinHash classes; see this post for example.

To fix this issue,

• add __and__ and __or__ methods on the MinHash class;
• add some tests to tests/test__minhash.py that confirms they do the same thing as intersection and __add__, respectively;

[bluegenes]

should this be closed? @hehouts @ctb

[hehouts]

yes! didnt think to do this, my bad

[ctb]

ok - for future reference, "Fixes #" in a PR will auto-close it, which is what should have happened, but I just noticed you had "Fixes issue #" which doesn't meet the very strict pattern that github looks for 😉