Case folding fixes (#133)

Case folding fixes (#133)

* Fixes allowing for “Full” folding and NFKC_CaseFold compliance.

* Only include C (Common) and F (Full) foldings from CaseFolding.txt. Removed S (Simple) since F & S are specified to be exclusive.
* Extend UTF8PROC_IGNORE to also ignore unassigned codepoints (such as \u2065) which are specified as being discarded by NFKC_CF.

* Document the changes to UTF8PROC_IGNORE in header.

* Add NFKC_CF helper function with documentation.

* restore old IGNORE behavior, add UTF8PROC_STRIPNA, rename to utf8proc_NFKC_Casefold, add a test

* success message

* test that IGNORE does not strip NA

* data update

* NFKC_Casefold shouldn't strip NA