Enable parallel builds

[greglandrum]

Doing conda build rdkit on windows takes forever since it doesn't use parallel builds. I think nmake isn't really capable of doing this, though there's some information here: http://stackoverflow.com/questions/601970/how-do-i-utilise-all-the-cores-for-nmake

Sounds like using JOM could work, and I know that creating vcproj files with cmake (using `-G"Visual Studio 1X". where X is whatever you have installed) and then building using MSBuild.exe works, but I'm not going to pretend to be an expert on building on windows, so I don't know what the implications might be.

Any thoughts?

[rvianello]

I remember trying to use MSBuild during the initial development of the windows recipe (also because this was/is the suggested tool in the rdkit documentation), but - for reasons that I can't atm recollect - I couldn't make it work, so I eventually opted for nmake.

The recipes already contain conditional code that depends on the combination of python/msvc versions so I think switching to MSBuild should be worth some testing. I can have a look at this while preparing the recipes for the upcoming release.