NF: added a new analytical response function derivation for Models that compute ODF with the r2 term
faster test
resolved conflicts and rebased with nipy-dipy-master
resolved conflicts
resolved conflicts
rebasing
rebasing
faster test
Modifications done following Ariel's comments
added and complemented documentation
NF: added a new analytical response function derivation for Models that compute ODF with the r2 term
remaining traces from rebasing
Merge pull request #261 from mdesco/r2_term_response

R2 term response function for Sharpening Deconvolution Transform (SDT)
Merge pull request #275 from arokem/restore-example

Restore example
DOC: A few more tweaks on this example.