Subset checks

Great project. Is there any plan to support fast subset checks?

To my understanding, currently the fastest way to check whether sorted array a is a subset of sorted array b would be

len(snp.intersect(a, b))==len(a)

the worst-case of which cannot be improved much. However, on average, one should be able to abort early once the first element of a is encountered that is not in b.

Cheers!