NF: added mean, axial and radial diffusivities for DTI (essential for DTI users and clinicians)
DOC: added documention
Making tests
Added tests for trace, mean, axial and radial diffusivities
ENH: Add the tensor metrics to the TensorFit object as autoattr's.
TST: Test that dti metrics get calculated on the multi-voxel case.

Also: fixed some typos from copy-pasting.
RF: all_zeros was not being used in any of these.
RF: Get rid of extraneous return variables.
Merge pull request #145 from arokem/mdesco-dti_metrics

Mdesco dti metrics
NF example for Tensor reconstruction
DOC minor updates
DOC QuickBundles Youtube highlight
DOC fixing minor mistakes and working on the presentation of the website
DOC added more info on masking for reconst_dti
DOC corrected language
DOC minor module addition
DOC added docstring for symm724
DOC started working on CSA example
simple update of the index table for examples
Minor print added for shape