Reimplemented unhash using Horner's method

No new feature, but improved code.

Thanks @jkramarz

Remove useless debug log

This release is trivial fix

Apply rebar3, hex.pm

Change build environment using rebar3, and also available in hex.pm

Supports about Erlang 18

• Fix build issue on Erlang 18
• Slight code cleanup
• Change return atom name

Adds encode_hex/decode_hex functions & code cleanup

• New encode_hex/decode_hex functions
• Code cleanup
• Some refactoring codes

1st stable release

1.0.0