Implement IAB Guidance on Unicode 7.0.0

[kjd]

Unicode 7.0.0 introduced support for the ARABIC LETTER BEH WITH HAMZA ABOVE (U+08A1) character which has been seen as controversial in some circles. While discussion continues on whether to amend the IDNA protocol or do some other kind of remediation for this character, IAB has recommended IANA essentially reverse publication of the 7.0.0 dataset on which the IDNA library relies. Therefore the library should revert to the next-to-last most recent data set which is from Unicode 6.3.0.

See https://www.iab.org/documents/correspondence-reports-documents/2015-2/iab-statement-on-identifiers-and-unicode-7-0-0/ for details.