Apparently, some code points fit both categories, for example U+0345
(COMBINING GREEK YPOGEGRAMMENI). Handle this fact when determining if
a code point is a final code point in a string.
This implements unconditional special case folding, and conditional
folding for non-locale cases. Worth noting that the only conditional,
non-locale special case is for converting an uppercase sigma to
lowercase.
The Unicode standard publishes the Unicode Character Database (UCD) with
information about every code point, such as each code point's upper case
mapping. LibUnicode exists to download and parse UCD files at build time
and to provide accessors to that data.
As a start, LibUnicode includes upper- and lower-case code point
converters.
