lib/libm: Add acosh, asinh, atanh, tan; get working with stmhal.
acoshf, asinhf, atanhf were added from musl. mathsincos.c was split up into its original, separate files (from newlibe-nano-2). tan was added. All of the important missing float functions are now implemented, and pyboard now passes tests/float/math_fun.py (finally!).