Use Premake to generate MSVC projects

[Attempt #2](https://github.com/ioquake/ioq3/pull/31)

premake5.exe must be in the path. It can be built from [here](https://bitbucket.org/premake/premake-dev). Unfortunately there's no official binary.

Tested on Windows 7 with MSVC 2008, 2010 and 2012.

As the commit message says, static SDL libs aren't compatible with the new renderer dll architecture, so I replaced them with the official import libs.