0.2.1 "Primordial Chaos"

This release mostly improves the random number generators; it adds StrangerRandom and Xoshiro256StarStarRandom, and fixes the nextInt(int, int) and nextSignedInt(int, int) methods (only the two-argument ones were broken, and only for some arguments). It adds a nice natural-text sort in NaturalTextComparator, using mostly this code as a basis. It also adds the Base class for numeral/base systems, which generalizes code that deals with decimal, binary, hexadecimal, base-64, and all sorts of other radices. I hope this is useful!