* Fixed tokenizer_string() off-by-one buffer overflow when processing string literals longer than the buffer limit.
* Fixed ubasic potential string buffer overflows by using snprintf instead of sprintf.
* Fixed ubasic label strings to use UBASIC_LABEL_LEN_MAX as buffer limit.
* Fixed ubasic string variables to initialize with zeros.
* Fixed compile errors when UBASIC_DEBUG_STRINGVARIABLES is defined.
* Added ubasic string variables user accessor API and unit testing for ubasic string variables.
* Fixed tokenizer_label() off-by-one buffer overflow when processing string literals longer than the buffer limit.
Steve Karg