Removed seqdata struct

Major refactoring of the code to remove the need for a seqdata struct
where all return computations are added.

Check __main__ of ViennaRNA.py for example of use.
Interface change

Removed the need to call ctypes on function calls. There is now a
proper interface requiring only the input of a sequence (no need for
dummy variables). All output is given together as a tuple.
Merge branch 'develop'