NEP: update NEP 19 with API terminology

[mattip]

With #13163 almost ready to merge, this updates the NEP with the terminology adopted there:

• the BitGenerator is the class that generates a stream of random bits
• the Generator holds a BitGenerator instance and can turn the stream of bits into ints and floats drawn from various distributions (uniform, normal, ...)
• the canonical function to produce uniformly distributed integers is integers (as an implementation detail it accepts an endpoint keyword to produce open or closed intervals)
• the canonical function to produce uniformly distributed floats is random, which parallels the use of random.random in the python (non-numpy) module.

[rkern]

LGTM.

[mattip]

Added an Updated field

[seberg]

Looks good, there are still a few occurances of "basic RNG" (and one "RandomGenerator"), those should probably be replaced as well?

[mattip]

a few occurances of "basic RNG" (and one "RandomGenerator")

Could you review again? I think I got them all

[seberg]

Thanks Matti, since Robert Kern likes it also, lets put it in.