Tighten up docs for \str_fold_case:n a little

Detail about the nature of folding and Turkic treatment should be given. The
fact that pdfTeX is 8-bit but we are only covering ASCII there is also
noted: UTF-8 overlaps with ASCII but not for chars >127 with e.g. Latin-1.


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@5157 de43f980-851b-0410-b2f7-c40aca1f87e0
Fix doc compilation

Too many spaces with \end{macrocode}!


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@5158 de43f980-851b-0410-b2f7-c40aca1f87e0