Win32: Add some MSBuild scripts to build from the command-line.

Might be handy for building PPSSPP quicker without having to open Visual Studio. These could easily be combined to build all 4 "platforms" at once (release/debug x86 & release/debug x64), but I figure it's more convenient to have them separate.

These will compile PPSSPP from the command-prompt, and package up the release and debug binaries up nicely in a new folder called bin-release, under the Windows directory in the source code tree.