Dev

Dear Dariusz,

This pull-request adds a new option to specify the derivation algorithm, either as BU or TD specifying bottom up or top down respectively. The top down algorithm is not as yet implemented but simply has a stub, which I will begin to populate. Additionally, as yet, this only has an effect if the --gendots is also specified. This is purely for testing purposes only and of course will be updated when the top-down algorithm is working satisfactorily.

allan