Support Org version 8.2.5h.

    Update mystyle.css.

    * Change h1 style.

    Update example.org.

    * Add use of IMPRESSJS_STYLE, IMPRESSJS_SRC and HTML_HEAD options as an example

    Add options IMPRESSJS_STYLE and IMPRESSJS_SRC

    * IMPRESSJS_STYLE - Path to a default CSS file for impress.js.
    * IMPRESSJS_SRC - Path to a JavaScript file for impress.js.

    Ignore the section indentations.

    Disable toc option

    * Slide can be broken when exported with toc.

    Modify commentary.

    Support the attributes used to position presentation steps.

    * data-x, data-y, data-z, data-scale, data-rotate, data-rotate-x, data-rotate-y, data-rotate-z

    Copy ox-html.el(Org version 8.2.5h) to ox-impress-js.el.
Update README.org.
Update example.org.