PyCdec lattice edge weights/features broken

[armatthews]

We updated cdec to allow a sparse vector of features rather than a single cost on each edge. PyCdec relies on storing edges in tuples, and while a double was fine in a tuple, a FastSparseVector is a C++ object and thus cannot go in a tuple, which is a python object.

The solution is probably to use a dictionary in the tuple, then have a function that converts a python dict to a FastSparseVector before throwing it back over the fence to the C++ side.

[ghost]

This renders the whole Python module broken. It is not possible to build a realtime system as described by [http://www.cs.cmu.edu/~mdenkows/cdec-realtime.html], as the module won't build and thus not install.