Experiment with adding header metadata output of slurp-csv and others

[metasoarous]

Some questions about how this would work:

• Would it just be the top level collection containers, or would it be included on individual records?
  • What are the performance implications here?
  • Would different levels be opt-in?
• How would this compose between calls? (Metadata doesn't always come out the other end of a transform the way you expect it to)
• Does this hint at there being a need for a higher level structure for passing information around?
• Does the order information captured by structs make this unecessary?

Value is that this would allow you to write out data in the columnar order it came in with.