Add BIN2HEX and HEX2BIN macros (trivial).
They're generally useful for lots of stuff, but especially for converting
to/from the compact 160 bit (20 byte) representation of SHA-1 hashes to
the "hex" representation (same as 'sha1sum' output), which is 40 bytes long.
Signed-off-by: Uwe Hermann <firstname.lastname@example.org>
Acked-by: Uwe Hermann <email@example.com>