Speech data object class to hold different features

[yoshua]

Choose a format and associated object class to hold the different speech features (some may be global to the sequence).

Coordinate with +Pascal Vincent on this (project-wide data organization).

[pascanur]

I've made a PR with a first draft with such a class. There are some planed changes (for e.g. make it export the entire interface required by pylearn2) though those should not break its currently functionality.

Proper documentation and example code (as well as more tests) are missing, though the simplicity of the class might make it already usable.