Update BEAM docs

Improve beam docs:
 * correct spelling
 * update per pandoc changes
 * capitalize titles
 * capitalize BEAM throughout and use "the BEAM" when referring to the virtual machine.
 * tweak grammar and phrasing
 * reformat build-tools-rebar3 section
 * add more links
 * re-wrap <para>s

Also update <programlisting>s
* normalize whitespace
* don't double quote homepage
* use $ in all shell snippets

doc/default.nix

@@ -26,7 +26,7 @@ pkgs.stdenv.mkDerivation {
       extraHeader = ''xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" '';
     in ''
       {
-        pandoc '${inputFile}' -w docbook ${lib.optionalString useChapters "--chapters"} \
+        pandoc '${inputFile}' -w docbook ${lib.optionalString useChapters "--top-level-division=chapter"} \
           --smart \
           | sed -e 's|<ulink url=|<link xlink:href=|' \
               -e 's|</ulink>|</link>|' \