bashtage/randomgen: Release 1.18

This release brings many breaking changes. Most of these have been implemented using DeprecationWarnings. This has been done to bring randomgen in-line with the API changes of the version going into NumPy.

• Dropped support for Python 2.7
• Synchronized with the randomgen merges into NumPy 1.17 and their fixes coming in 1.18
• Added support for SeedSequence (and NumPy's SeedSequence).
• The .generator method of the bit generators raise NotImplementedError
• The internal structures that is used in C have been renamed. The main rename is brng_t to bitgen_t
• Rename RandomGenerator to Generator.
• Rename randint() to integers().
• Rename random_integers() to integers().
• Rename random_sample() to random().
• Change jump which operated in-place to jumped() which returns a new BitGenerator.
• Rename Basic RNG to bit generator, which has been consistently applied across the docs and references
• Add the integer-based SIMD-based Fast Mersenne Twister (SFMT) generator SFMT.
• Add the 64-bit Mersenne Twister (MT64) generator MT64.
• Renamed Xoshiro256StarStar to Xoshiro256 and Xoshiro512StarStar to Xoshiro512