Cythonized version of streamlines' resample() and length() functions.

I made a cythonized version of the resampling and length functions found in `tracking/metrics.py`. As suggested by @Garyfallidis, I put these new functions in `core/streamlinespeed.pyx` accessible through `core/streamline.py`.

I made a minor change to the Makefile and setup.py to add the compilation of the new cython file. Also, regarding the language use for compiling Cython, I changed it to C++ instead of C since I needed `vector` from C++ std and also it was not breaking anything except one thing that I also fixed (see commit logs). If you don't want to change the compiler for Cython, I can set it only to compile `core/streamlinespeed.pyx` instead.
OK - I am just worried about making `core` a dumping ground for stuff that
doesn't clearly belong anywhere else. I think that `core` should be
reserved for stuff that is required by all the other modules. Maybe this is
the case here. What is the typical use-case for resampling tracks?
Segmentation? Maybe this should go under `segment`?


On Wed, Jul 2, 2014 at 7:06 PM, Eleftherios Garyfallidis <
notifications@github.com> wrote:

> In dipy/core/tests/test_streamline.py:
>
> > @@ -0,0 +1,279 @@
> > +from __future__ import print_function
> > +
> > +import unittest
> > +import numpy as np
> > +
> > +from nose.tools import assert_true, assert_false, assert_equal, assert_almost_equal
> > +from numpy.testing import assert_array_equal, assert_array_almost_equal, assert_raises
> > +
> > +import dipy.core.streamline as dipystreamline
>
> The idea here is that we can have in dipy.core.streamline different ways
> to represent streamlines. Tracking for me is more about creating
> streamlines rather than the streamlines themselves.
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/nipy/dipy/pull/382/files#r14494402>.
>