Added README on more advanced test running
Added dimensionality checking for connections.

- added explicit checks with helpful error messages for connections
  with mismatched dimensionality
- Nodes now have separate size_in and size_out parameters
Moved Connection size checks to separate functions
PEP8 fixes
Fixed node function argument error for python 2/3
Removed unused import
PEP8
Removed Connection.decoders (fixes #251).

- also improved documentation for Connection class.
Damn PEP8