Added support for the following:
1) Parsing of Scientific Durations (ANSI Smalltalk syntax);
2) Parsing of Calendar/Civil Durations (ISO 8601 syntax--which requires support for fractional element values);
3) Calendar/Civil durations with fractional element values (years, months, days, seconds)--because of #2;
4) Date/Time arithmetic involving fractional elements (years, months, day, hours, minutes, seconds)--because of #3;
5) Added 2007-01-02 as a NYSE closure date (Day Of Mourning for US President Gerald Ford.)
6) Changed some class and category names for compatibility with Monticello.
7) Some other minor improvements.