DOC - add info on how to change default tempdir (multiprocessing).
Merge pull request #440 from gabknight/doc_multiprocessing

DOC - add info on how to change default tempdir (multiprocessing).
NF: generate config.pxi file with Cython DEF vars

Eleftherios needs to do conditional compiling depending on whether
openmp is present or not.

Following the recipe in
http://stackoverflow.com/questions/3826458/cython-conditional-compile-based-on-external-value
-- build a ``config.pxi`` file containing DEF variables that can be used
in extension code.  For example, with the code here, a Cython extension
could include the following:

    include "config.pxi"

    IF HAVE_OPENMP:
        cimport openmp
Merge pull request #445 from matthew-brett/conditional-compiling

NF: generate config.pxi file with Cython DEF vars
NF: unique rows of an array.
NF: Added a crutch function. This will need to be removed later on.

And replaced with `move_streamlines`, but I am defering that until I get a
sense of what is happening here.
NF: Added a first-pass implementation of LiFE.
RF: Thinking about simplifying this.

Maybe use dipy.sims.voxel directly?
WIP: Completed the mapping function voxel2fiber, inclduing test.
Matrix allocation more-or-less working.
WIP: Still working out how to create this model.
NF: Added Sparse SGD algorithm for solution of the LiFE equations.
TST + BF: Make sure that input to np.gradient is an array.
RF: Move down the fit function.
RF: docs
Might not need to isotropic matrix, if we treat that as a mean.
RF: seems to be running through now. Need more tests.
TST: Fix typo in test. Reinstate the Fit test, but need something more rigorous
BF: Need to be a little stricter to be able to round-trip.
RF: Moving stuff around a bit, and starting to cythonize voxel2fiber