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' - v2.0