[WIP] Bundle lgamma and deps from fdlibm for MSVC

Under MSVC, `expected_mutual_info_fast` fails to compile because `lgamma` is not part of that distribution of `math.h`.  Here is my attempt at bundling it. 


This now correctly builds on both windows and on my MacOS X.  The scores seem always `nan` however.

<del>There are no test failures related to `expected_mutual_info`. However, the following need to be checked:

1. Are the `expected_mutual_info` tests good enough that their passing means lgamma works properly? Should we explicitly test the bundled `lgamma`?</del>

2. Does this break anything on other platforms? (for this I need your help)

3. A (maybe) worrisome fact is that `fdlibm.h` includes `math.h` and I only bundled the symbols that were undefined on Windows with MSVC.  It needs the two implementations to work together.  I don't see why they wouldn't, these things are standardised, but input from people who know about this sort of thing is very welcome.