Improve new developer experience
Update README and hctstart.cmd tools to help new developers.
Update README
* Add instructions on how to setup the build environment
from the command line.
* Add note to install common tools for c++ to get the atl headers.
* Change cmake download to point to cmake 3.4.3. Version 3.4 did
not work for me (it could not find the Visual Studio compiler tools).
Modify hctstart.cmd
* Explicitly check for the d3d12.h header from the 10240 windows kit.
Without this early check we get a build error much later.
* Check for cmake version 3.4.3 and warn if not found.
Update gitignore for visual studio code temporary files.
David Peixotto
Marcelo Lopez Ruiz