Generate PDFs directly instead of SVGs

[timparenti]

The additions in c34199f summarize workarounds employed by @catern to convert the output of the SVG generators into PDFs suitable for printing.

We should probably be aiming to generate PDFs directly. Python packages exist to help with this, including pyfpdf and pdfrw, but those don't seem to have been updated in a while.

[haoxuany]

One other option is to generate PostScript files for easier printing, since it has a much simpler format definition than PDFs.
One package I found is PyX. It can generate Extended PostScripts and PDFs. However, it seems to be geared mostly towards latex graph generations. One way to draw the poster is to manually write the draw instructions, which may or may not be what we want.

[timparenti]

Awesome! PostScript would definitely be a suitably reasonable intermediate.

For additional convenience, ghostscript looks like it can handle basic PostScript to PDF conversion; maybe it'd be good enough for our needs.

[timparenti]

I just came across cairosvg, which may actually be able to handle this. It has a fairly comprehensive page about the various features of SVG that it supports, and at a cursory glance it seems to be able to handle most of what we'd need.

I'm having trouble getting it to successfully install via pip, though.