LiFE

This is just to let you know that I am working on an implementation of the Linear Fascicle Evaluation algorithm, described in our recent paper: http://www.nature.com/nmeth/journal/vaop/ncurrent/full/nmeth.3098.html

There might be an opportunity to speed things up, using cython. In particular, I am thinking about ways to speed up both sl_signal and voxel2fiber, and any suggestions on that are most welcome. 

Rename to transform_streamlines.

@arokem in my SLR PR (#446) I have the same function using nibabel's apply_affine.
But I have this function in dipy.tracking.streamline where I think it is better suited.
Would you mind moving this function there? I don't mind using internally
move_streamlines or nibabel's apply_affine. As long the performance is similar.
However, I have to say that move_streamlines is not a good name because
move is only about translation but here we can apply all affine transformations.
I had made this remark to @MrBago from some time ago in his connectivity matrix PR
but he never renamed it. Missed this comment somehow. 

So, can we move those functions to dipy.tracking.streamline and rename move_streamlines and transform_sl?