No emcc exe

This pull request builds on the feature by jgranick to use 'emxxx.bat' files to route to 'python emxxx'. This and the added support for response files in emscripten makes the whole juj/vs-tool emxxx.exe wrappers obsolete, and I can remove the manual build steps that were previously needed to set up emscripten on Windows for use with cmake of VS2010.