Mammoth

* Add basic support for Markdown. Not all features are currently supported.

* Add default style mappings for builtin footnote and endnote styles in
Microsoft Word and LibreOffice.

* Allow style mappings with a zero-element HTML path.

* Emit warnings when image types are unlikely to be supported by web browsers.

* Update jszip to 2.4.0.

* Add support for endnotes.

* Update license-sniffer to fix license comments in mammoth.browser.js.

* Update bluebird dependency to fix operation in web workers.

* Add support for superscript and subscript text.