build LAMMPS for Windows via Visual Studio

Ilya Valuev (JIHT, Moscow, Russia), provided
some Windows support for building LAMMPS from
source code via Visual Studio project files.

We released these today in a 15Jun11 patch.

So if you run on Windows boxes and use Visual
Studio and want to build or develop in the current LAMMPS
using the VS IDE, this should be helpful to you.

You can also still download pre-built Windows LAMMPS
executables from the download site, but they will
always be somewhat out of date, since we don't build
them very often.