- Changed 'transform' method to use ValueInfo throughout. This fixes a number of obscure bugs
- Changed the 'add' and 'sub' methods to default to "now" rather than null. This means null passes through rather than being interpreted as the current time, to be consistent with other date tools
- Also changed the 'add' and 'sub' methods so that they operate correctly with invalid date strings
- Added tests for the class; improves #66
- Modified TTRSS tests because the "iso8601" format string in ValueInfo is different from Date's older format