NF: added a new analytical response function derivation for Models that compute ODF with the r2 term
faster test
Modifications done following Ariel's comments
added and complemented documentation
DOC: Working on RESTORE example. Enhanced DTI docstring.
WIP
ENH: enforced peak_directions to calculate the peaks on the min_max normalizated ODF
BF: corrected tau parameter
TEST: updated test for peak_directions
Corrected peak_extraction script
Updated default peak_values for reconst csd parallel
NF: added function for peak visualization
TEST: added test for fvtk.peaks
DOC: updated CSD example to show the peaks
TEST: tiny cleanup
BF: normalized odf values should be used for search descending as discovered from Bago
RF - fix peak_directions
Merge pull request #18 from MrBago/peak_directions_update

RF - fix peak_directions
BF: Consider the absolute value of the residuals.
DOC: RESTORE example with data.