tools for generating testcases and checking ulp error of math functions

(needs cleanup)

gen: math functions implemented with mpfr

mgen: math functions from libm

check: compare input to libm and report errors

check asinh in the [0.125,0.5] domain over 100k points and report >1.5ulp errors:

./rnd -a 0x1p-3 -b 0x1p-1 -n 100000 |./gen asinh |./check asinh 1.5