Remove the pdfjs submodule, since we can't track it usefully.
Re-import pdf.js as a static copy.

These files are from commit f6113b59e373c87042b1c41266f3688bd2579b3b on the
gh-pages branch of the pdf.js Github repo. This branch seems to get
overwritten nightly, so importing it as a submodule was ineffective. I've just
included the static files, which were dated 2013 Sep 10.
README.md: touchups