Building using mingw64 on Windows using Python 3.X x64

[mcvicuna]

The instructions in the wiki are a bit vague and I don't believe they work with x64 versions of python.
Some issues I had:

• Building boost python.
  There is a lot of information on the web and it took a bit to find one that worked. I used instructions from http://alexadotlife.com/blog/2013/10/13/boost-python-mingw64/ to get it working.
  The missing steps from the wiki are the command to make the import library in a form mingw64 will understand and the boost build options needed to build 64bit boost-python.
• Buidling pygmo
  CMake for some reason couldn't or wouldn't find the python import library so I had to manually specify it as "C:/PythonXX/libs/libpythonXX.a". I also added -DMS_WIN64 to CMAKE_CXX_FLAGS.