A pure Erlang IDNA implementation.

An attempt will be made to read from priv/UnicodeData.txt. If the file does not exist,
it is downloaded from unicode.org, and an attempt is made to save it to the above filename,
though no checking is done as to whether or not this succeeded.

Quick start:

  $ make
  ...
  $ erl -pa ebin
  ...
  1> inets:start(), idna:start(). % downloads UnicodeData.txt from unicode.org
  ...
  2> Domain = xmerl_ucs:from_utf8("www.詹姆斯.com").
  ...
  3> idna:to_ascii(Domain).
  ...

Reference material:

  RFC3490 (IDNA)
  https://www.ietf.org/rfc/rfc3490.txt

  RFC3492 (Punycode)
  https://www.ietf.org/rfc/rfc3492.txt

  addressable (Ruby URI implementation)
  https://github.com/sporkmonger/addressable

  punycode4r (Ruby punycode implementation)
  https://raa.ruby-lang.org/project/punycode4r/

  Unicode Character Database
  https://www.unicode.org/Public/UNIDATA/UCD.html

  UAX #15 (Unicode Normalization Forms)
  https://www.unicode.org/reports/tr15/