Add emacs lisp API wrappers.
Proof of concept: commands for listing and browsing projects.

To get started:

  (add-to-list 'load-path (expand-file-name "~/path/to/your/dx-toolkit/src/elisp"))
  (require 'dx)
  (setq dx-auth-token "...")
dx-list-projects: factor out major mode, add keymap, browse proj link
Add hook dx-list-projects-mode-hook.
dx-browse-project: support browsing subfolders too.
Add some getting-started docs.
dx-browse-mappings.
Refactoring/navigation for dx-browse-mappings-mode.
Update copyright years.