While these casts can be implemented by casting via uint, the resulting code is
less readable than code that uses direct casts.
library/uint16.m:
library/uint32.m:
library/uint64.m:
Add cast_from_uint8/1 and cast_to_uint8/1 to these modules.
NEWS:
Announce the above additions.
tests/hard_coded/Mmakefile:
tests/hard_coded/uint{16,32,64}_uint_casts.{m,exp}:
Add tests for the new casts.
