Add support for excluding files in the build directory

[no-preserve-root]

Most likely, these files are generated or downloaded external code. In the former case, licensing information should be generated by the code generator; in the latter, the license should remain untouched.

This is controlled by the extension property “includeBuild”, defaulting to true (this could be change to false to keep the former behavior). Personally, I have not encountered a situation where I would want generated files to be rewritten.