Log Message:
libunibreak: add version 6.1

This is libunibreak, an implementation of the line breaking and
word/grapheme breaking algorithms as described in [Unicode Standard
Annex 14][1] (UAX #14) and [Unicode Standard Annex 29][2] (UAX #29).

As of February 2024, Unicode 15.0 support for line breaking, as well as
full Unicode 15.1 support for word/grapheme breaking, is provided.
There is currently no plan to implement full Unicode 15.1 support for
line breaking, mostly because tailoring for Brahmic scripts, as
described in LB28a of UAX #14-51, is problematic within the current
framework.