One file output per model

[MikeLippincott]

          Given the sheer quantity of figures you're generating, I wonder if it's actually not worth writing the figure to both `html` and `png`.

I'm now thinking that you probably should just output a single PDF. (so no html or png).

I like the thought of having this else statement, which we can use in the future, for outputting targeted figures.

For right now, in this exploratory phase, my fear is that all these additional htmls and pngs will do is cause the repository to over bloat and only provide minimal value.

The single (or few) PDF would solve the value problem (by nature of being there) and would remove bloat. Ideally, our repositories are small.

Originally posted by @gwaybio in #16 (comment)

[MikeLippincott]

specifically for the linear modeling keep the output to one file per model