register_methods(): "user" -> "user-supplied"

[HenrikBengtsson]

Formally, I think "user" in:

dqrng/R/register_methods.R

Lines 71 to 72 in a474001

	both = state$RNGkind <- RNGkind("user", "user"),
	rng = state$RNGkind <- RNGkind("user"))

should be spelled out as "user-supplied" per help("Random"). One advantage, would be that it's easier to search for code and packages that use "user-supplied" - more specific than "user".