Docs and make subclass-able
Docs and make subclass-able

blink1073/jupyter-js-filebrowser,jupyter/jupyter-js-filebrowser,jupyter/jupyter-js-filebrowser,blink1073/jupyter-js-filebrowser,jupyter/jupyter-js-filebrowser,blink1073/jupyter-js-filebrowser,jupyter/jupyter-js-filebrowser,blink1073/jupyter-js-filebrowser,jupyter/jupyter-js-filebrowser,blink1073/jupyter-js-filebrowser