Per-section poster designs

[timparenti]

I've already started some work on this privately, but I feel this blocks on #3 and #10.

The idea is that there could be posters for each "section" of the talk series which invert the colors of the main poster for the whole semester. For example, if the first section of talks appear yellow on the black background in the main poster, another poster focusing on just that section would have black text on a yellow background.

Since there would be fewer talks on each of these posters, they would necessarily appear larger (like #10) but could probably also have short descriptions appear as well.

[timparenti]

This is no longer blocking on other issues, but it will be easier if the constants in the script are reorganized, and magic numbers are further removed. So I'm starting work on that incrementally in the meantime.

[timparenti]

My branch for this has become a little stale, but the good news is that a lot of the groundwork commits I wrote in February to help support this were cherry-picked into master and/or reworked to support the Makefile and #14; namely be2596f, 9f0f29b, and dbc54aa.

I'll see if I can't rebase this into something useful before we need to more actively promote the second "section" of the Fall 2015 series in late September.