Feature Request: TutMain options for dumping tut code blocks to external file

[metasim]

Sometimes when having to fix a bunch of tut code after a refactor, it's easier just to have the code bits back in an independent Scala file to fix it up and then paste back into the tut doc. This would help with that process.

[metasim]

This may be covered in some part by sbt-scaliterate.