char and string folding

[alexshinn]

R6RS provided operations to alter the case
of strings and characters (upcase, downcase, titlecase
and foldcase) using locale-independent Unicode
mappings. Do we provide equivalent mappings,
and how do they behave in the different char sets
we may allow per ticket #23?

[cowan]

I recommend that we provide these. The character procedures should use Unicode simple mapping and folding (which is 1-1). The string procedures should use Unicode full mapping and folding, which is usually 1-1 but sometimes not: "ß" upcases to "SS" and folds to "ss".

If the proper character is not supported by the implementation, the procedures should leave it alone: some Unicode lowercase characters have no uppercase equivalents, but coherent subsets of Unicode will usually provide both lower and upper case versions of all characters.

[cowan]

The WG voted to place these features in a module.