(UNSIGNED): Renamed from STRTOUXMAX_UNSIGNED.
(verify): New macro.
(INT): Renamed from uintmax_t.
(strtoumax, strtoull, strtoul): Remove.
(strtoimax, strtol, strtoll): New macros.
(strtoimax): Renamed from strtoumax. Interchange signed with unsigned.
Verify sizes at compile-time, not at run-time.
Prefer strtol to strtoll if both work.
(main): Remove.