.org: add org-mode as a submodule

We plan to include a Makefile that can leverage this to compile *.org
files directly to PDFs.
9/foss.in: hide notes by default
{9,10}/foss.in: fix .gitignore
{9,10}/foss.in: Add build.el, Makefile

Write a clever Emacs Lisp script to use .org/ from the toplevel
directory to org-export-as-pdf.  Wrap it in a simple Makefile, taking
care to generate bibliographies where applicable.
README: update build instructions

Also create a toplevel .gitignore.