Add a batch file for invoke premake

This change adds `./premake.bat` to the repository, which users in Windows (64-bit) can use to conveniently invoke the copy of premake that is pulled via the `slang-binaries` submodule. It should be possible to pass whatever options you passed to `premake5.exe` through to `premake.bat`. E.g., if you invoke:

```
.\premake.bat vs2015
```

then you should get the desired results for the project/solution files we want to check in.

0 files changed, 0 insertions, 0 deletions