Add support for escape Parser directive

[mgansler-intland]

https://docs.docker.com/engine/reference/builder/#escape

This is very useful when writing Dockerfiles for Windows Containers.

[asbjornenge]

Would gladly support if you can build us a PR 👍

[AssimaSA]

A sea of pink, in windows container docker files. I second on this request.

[katlimruiz]

+1

[princemaple]

No idea how this could be implemented... PRs welcome!