documentation: provide some explanation of "case folding"

[robx]

I just spent quite a while digging, first through the source, finally ending up at http://hackage.haskell.org/package/text-1.2.4.0/docs/Data-Text.html#v:toCaseFold while trying to figure out what the result of toCaseFold is actually like.

It would probably be useful to others to do one or more of the following.

• add a sentence in the general parts of the documentation noting that case folding is mostly but not quite lowercasing (perhaps with a link to a more detailed explanation)
• in the documentation of foldedCase, explicitly state that the result depends on the FoldCase instance (instead of just a "see also")
• document the behaviour of the individual FoldCase instances

[jappeace]

I don't think this is maintained.

[jappeace]

@basvandijk please add me or robx as maintainer on hackage, my hackage name is Jappie (case sensitive).

[robx]

(I'd rather not take on a maintainer role.)

[jappeace]

presumably this is the source of the naming: http://www.unicode.org/Public/UCD/latest/ucd/CaseFolding.txt
I intend to link to that in the docs