Fix for issue 46: Parsing error - Fri (.)*

In general, tokens that are substrings should be ignored.
Known issues: afri, zfri, afriday, zfriday are still parsed for the following reasons:
- 'afri' or 'afriday' are lexed as FRIDAY, with AM dissapearing somewhere
- 'zfri' or 'zfriday' are lexed as UTC FRIDAY and are then parsed into a valid date