More clarifications to file format spec
Removal of an inconsistency between spec and code
Yet further corrections to file format
Yet another correction to file format
Made child classes of Command do file I/O directly
Added a parsing helper to Event.cpp
Refined preparser for strings
Fixed bug in Dt::addMonths
Added Next and Prev functions to Event

Fixed a bug where a lack of EndOccurrence tag would make the program
hang