Convert corr3 into the new API about treecorr

[rmjarvis]

For what it's worth, the old code for doing the 3-point calculation is now in the directory old_code (on master for now, will be included in release version 3.2).

I'm afraid it's not nearly as user friendly as the 2-point code. It's an executable program - correeeb -- not a python module. And it doesn't even use parameter files. All the parameters about the binning and such are in CorrEEEb.cpp, which you have to change by hand and then recompile.

Plus the documentation is not nearly as good, although there is a Read.me file that explains how to run it.

And finally, it only works in Euclidean coordinates, not RA/Dec, so you'll need to project your positions onto a tangent plane. (Which the python version of treecorr can do for you, I should point out.)

So if you want to try to use it, you are quite welcome. However, if you can wait for this issue and #4 to be done (goal for both: Summer 2015), it may be significantly easier to use at that point.

[rmjarvis]

Done. Just NNN, KKK, GGG so far (which is already more than the old code could do). Including features like setting the min/max u, v, and doing things in spherical coordinates. Will be in v3.2.