mldata 1.0

Adds : 
- Datasets loaded lazily of in memory
- Metadata to keep track of datasets
- Configuration files to index datasets
- Utilities to save/load/remove datasets
- A first basic CSV importer to create datasets
- Full docstring docs
- Test suite
If `lazy==False` do we want `data` to be a ndarray? Right now it is a `HDF5 dataset` but still supports iteration and indexing as numpy.