Convert slides to PDF

[AmeliaBR]

With the rush to get everything posted, many of the slides links are powerpoint or ODP files, which need to be downloaded and opened in compatible software. For archival purposes, it would be better to have PDF if we can't have HTML.

Since the Powerpoint & ODP files are already in the repo, it probably makes sense to leave them up, and add the PDF versions as alternatives, which requires some more template tweaking to support multiple links for a talk.

[nchan0154]

I have converted all the pptx files we had to PDF and tweaked the templates a bit to support multiple links in a way that's hopefully a little less cluttered. We are still missing

• Bocoup's Review of the MapML Proposal by Simon Pieters (hosted on slides.com, may need him to export)
• The MapML Proposal - Part Two by @prushforth currently has a youtube link instead of slides :)