Merge pull request #230 from arokem/tensor_predict

Tensor predict
WIP: Initial commit of some DKI-related stuff.
TST: Starting to test the implementation of a by-direction ADC calculation.
NF: First-pass implementation of by-direction ADC. Still needs more testing.
DOC: Documentation of the ADC calculation.
TST: Another, more quantitative test of ADC calculation.
Even more testing.
ENH: Much more work on DKI, based on Jensen, Helpern, Lu et al.
DOC: mostly added details to documentation of data-sets.
ENH: Added some DKI-type data. Refactored the calculation to rely on eq 38-39.

This is in Jensen and Helpern's paper. The idea being that you compare the
estimate of ADC in different b value to calculate a 'real' ADC and then use
that to bootstrap the calculation of ADK.
RF: Adapt to new prediction API from TensorFit.