Add method for graphing facet results

Pie in the sky idea.

Maybe any selection of JSON results. Imagine looking at wp.com stats endpoints and immediately graphing them.

Would be great to be able to take results and quickly create an image from them.

Don't need to go crazy though, #14 enables using spreadsheets.

The issue names no source file, test, entry point, accepted input format, or image output. First inspect the repository to locate result-handling entry points and existing tests, then clarify which JSON facet selections and image formats are required. Done should mean a defined, tested way to turn selected facet results into an image.

Written by the indexing model from the issue text.