Hex encoding functions on the binary module

Hello everyone,

I propose to add the encode_hex/1, encode_hex/2 and decode_hex/1
functions on the binary module[1].

Dealing with the hex format is frequent in many codebases. At this time,
we all copy-paste similar helpers in our codebases to encode and decode
a hex-encoded binary.

It's why I suggest enriching the binary module with these functions.

I've added these functions on the binary module because it makes sense
to me, and it avoids polluting the global namespace with a new
module. Maybe create a new module called hex, for example, is a better
solution.

I tried as much as possible to follow the contribution guide. Don't
hesitate to tell me if I made a mistake somewhere.

Regards,

-- 
Bryan Frimin
https://www.frimin.fr
[email protected]

[1] https://github.com/erlang/otp/pull/3014