Add support for building self-contained presentations and for passing extra variables to pandoc

[kalbasit]

When selfContained is false (default), the reveal.js files are now absolute and the reveal.js symlink is removed. This allows the HTML files to reside in any sub-folder without having to maintain relative dependencies.

When selfContained is true, the resulting HTML file will have all assets inlined, that includes all reveal.js files as well as any embedded images in the markdown presentation.

Extra variables can be passed in the extraPandocVariables set. For example, to use a different theme, pass extraPandocVariables = { theme = "sky"; };. Note that when using a reveal.js theme that is not the default theme and has selfContained enabled, Pandoc requires network access and this will not work with the sandbox enabled. You must disable the sandbox with nix-build --option build-use-sandbox false.

[kalbasit]

Here's a shell.nix that I use to provide a wrapper around nix-build that disables the sandbox without having to type in manually every time. Should I put it in the README?

{ pkgs ? import <nixpkgs> {} }:

with pkgs;
with pkgs.lib;

let
  nixBuild = pkgs.writeScriptBin "nix-build" ''
    #! ${runtimeShell} -e

    ${getBin nix}/bin/nix-build --option build-use-sandbox false "$@"
  '';
in

stdenv.mkDerivation {
  name = "presentations-dev";

  buildInputs = [ nixBuild ];

  phases = ["nobuildPhase"];

  nobuildPhase = ''
    echo
    echo "This derivation is not meant to be built, aborting";
    echo
    exit 1
  '';
}