Added the option to correct BC-dates, since the year 0 is needed by the rwl-format, but not in the FH-format. The correction moves BC-dates one year forward, if the option is set to TRUE (default is FALSE).
Sometimes only the DateEnd is given in a FH-file. Therefore the edited function only looks at the DateEnd and calculates the DateBegin if this is missing. This also moves the check of the length/start year to another part of the function
Some suggested improvements: