refs #562 - Fix backslashes acting as escape chars

Trailing backslash in `%CASPER_PATH%` was escaping closing quote in `--casper-path`.

This changes backslashes in `%CASPER_PATH%` to forward slashes. Same with `%CASPER_BIN%` to be consistent.

I also removed superfluous `%ARGV%` variable to avoid potential problems with batch failing to properly send full cli params.