Embedding API

[capnrefsmmat]

I should make it easy to embed regressomatic plots in any HTML document.

It's already fairly easy, as evidenced by regression.html, but I should give a simple API to:

• Specify the axes labels, data set, diagnostic to show, and statistics to provide
• Select an empty element to dump them into.

Data could be provided as a JS array or as the URL of a CSV file, in which case we'd fetch the data and axes labels automatically.

This would require making a wrapper function that loads the data, populates the empty element with spots for regression and residuals, and calls regressionPlots.