IDNA 2008 compliance

[zp-sd]

1) Implement label validation as stated in https://tools.ietf.org/html/rfc5891#section-4.2

2) Based on https://tools.ietf.org/html/rfc5891#section-4.1

a string enters the IDNA registration process as
described in this specification, it MUST be in Unicode and in
Normalization Form C

However the code uses unicode_util_compat:nfkc.

3) See also UTS #46, especially http://unicode.org/reports/tr46/#Processing.

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Maybe support parameters as ICU 60.2 does (http://icu-project.org/apiref/icu4c/uidna_8h.html), This lib was used in https://github.com/benoitc/erlang-idna-nif.

[benoitc]

68f03ab9e89e276e3f657902a6bc8f03e014423c handle IDNA mapping and options based on http://unicode.org/reports/tr46/#Processing. .

Current tests pass.

[benoitc]

I started to add the label validation.

The following need to be validated according to rfc5891 :

• [x] check NFC: Label must be in Normalization Form C
• [x] check hyphen: The Unicode string MUST NOT contain "--" (two consecutive hyphens) in the third and fourth character positions and MUST NOT start or end with a "-" (hyphen).
• [x] Leading Combining Marks: The Unicode string MUST NOT begin with a combining mark or combining character (see The Unicode Standard, Section 2.11 Unicode for an exact definition).
• [x] Contextual Rules: The Unicode string MUST NOT contain any characters whose validity is context-dependent, unless the validity is positively confirmed by a contextual rule. To check this, each code point identified as CONTEXTJ or CONTEXTO in the Tables document RFC5892 MUST have a non-null rule. If such a code point is missing a rule, the label is invalid. If the rule exists but the result of applying the rule is negative or inconclusive, the proposed label is invalid.
• [x] check BIDI: label contains any characters from scripts that are written from right to left, it MUST meet the Bidi criteria rfc5893