Changes to ScheduleGenerator and BusinessdayCalendars:

[NiklasRodi]

• BusinessdayCalendar::createDateFromDateAndOffsetCode(): Make method non-static to enable business day rolling; add business day rolling (indicated by 'b' or 'bd')
• BusinessdayCalendar::createDateFromDateAndOffsetCode(): throw exception if unit char is of unknown type instead of trying to parse as Act/365
• BusinessdayCalendar: moved some documentation to BusinessdayCalendarInterface
• BusinessdayCalendar...: Added simple toString() methods
• ScheduleGenerator: Reduced some code duplication in createScheduleFromConventions() method by letting them better call each other