Support multiple paper sizes

[timparenti]

Per @stroucki on IRC (2015-01-20), "the talk poster is rather large to post and not be rude to others". We should be able to support a few paper sizes in addition to the standard 17"×11" tabloid size; namely, 11"×8.5" for smaller posters.

With that, we could also do 8.5"×5.5" half-sheets or 5.5"×4.25" quarter-sheets as needed, since those are the same ratios as the above.

[stroucki]

If we used ISO 216 paper sizes...

[cpreseau]

... We'd never be able to get Catherine to print them for us ;)

[lroop]

I second this. Shelby noticed the same thing postering in Hamburg last night, the bulletin boards there are tiny. The 11x17s are still reasonable and eye-catching for larger bulletin boards like the massive ones in Wean.

[timparenti]

Current workaround for the letter-size versions requested by @catern (particularly "grayscale" versions per #14):

• Print to Adobe PDF from Google Chrome with margins set to 0" on the left and right; 0.4" on top and bottom.