Changes since 2.1:
* Unicode 15 update. Added unicode_derived_<name>() lookup for derived core properties. Added unicode_general_category_lookup() for general category lookups. Fix GB11 rule.
* configure.ac: gcc 12, autotool updates.
* Fix compilation error on CentOS 7.
* unicode_bidi.c: Implement unicode_bidi_combining(). Implement canonical and compatibility decomposition and canonical composition.
* unicode_bidi.c (unicode_bidi_needs_embed): Make its return code what its documentation says its return code is.
* Implement unicode_bidi_needs_embed(), unicode_bidi_cleaned_size(), unicode::bidi_override, unicode_bidi_calc and unicode_bidi_calc_levels return a unicode_bidi_direction object, to indicate whether the computer paragraph embedding level was explicitly computed or defaulted.
* courier-unicode-version.m4: split version checking macro into its own m4 file.
* unicode::bidi_calc - an empty string with an explicit embedding level should return the requested embedding level.
* unicode::iconvert::convert, fix uninitialized variable.
* Implement bidirectional algorithm, canonical or equivalent character mappings.
* Unicode 13 update. Adds lookup of EastAsianWidth property, emoji property lookup, adds an alternative sequence-based grapheme API that handles multi-character emoji rules.
* Add bidi property lookups.
* Makefile.am: Regenerate docs due to broken man page links.
* unicodebuf.c (unicode_buf_remove): Bug fix.
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