Cleanup and minor changes to improve integration with internal projec…

…ts (microsoft#3199)

* Cleanup and minor changes to improve integration with internal projects

Adds -Debug option to hcttest.cmd

* Case insensitive compare for -Debug and -Release flags in hctbuild and hcttest

Enable TAEF path specification via environment variable (microsoft#2778)

Added section on where to get interim releases

Added section on where to get interim releases

Bump up version 2018, remove print for shader model 6.2