Add options to utf8_idpb() to allow other types of utf8 code

Currently hardcoded now, but this can be expanded in future to be toggled.
UTF8IDPB_NOZERO Allows for 0 encoded as a non-zero utf8 0xc0:0x80 char.
UTF8IDPB_LIMIT - Today's utf8 is within values of {0..0x10FFFF}.
UTF8IDPB_SURROGATES enables utf16 surrogate values.
see developer-list - [Fontforge-devel] Failed to build again

To resolve problem with this error

cvundoes.c: In function 'UndoToString':
cvundoes.c:3927:5: error: implicit declaration of function 'SFDDumpUndo'