[MRG] Added lgamma Cython interface to utils for MSVC

**Without this we cannot build WIndows release binaries!**

*Current status*:
Works correctly on Travis
Works correctly on my MacOS X Mountain Lion with Apple clang 4.0
Works correctly on my Windows 8 VM with MSVC 15.00 (from Visual C++ Express 2008, as usual)

*The backstory*:

`lgamma`, the logarithm of the gamma function, is not available in `math.h` under MSVC, which makes the current master not build under Windows.

In another PR (#1526) I tried bundling more and more of `fdlibm`, until I gave up, seeing how it gave wrong results on windows. Now, instead of bundling a whole library, <del>I got everything that's needed in a single C file, and wrote a Cython wrapper for it</del> I used John D. Cook's LogGamma function as suggested by @larsmans.

It builds and returns accurate results on both my MacOS X as well.

The best thing is that it doesn't depend on endianness anymore, so this should be good to merge!