Specification: http://www.w3.org/TR/WOFF2/
Browser Support: Chrome 36+

Other links:

• http://www.w3.org/TR/WOFF20ER/
• https://code.google.com/p/font-compression-reference/wiki/testing_woff2
• https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/j27Ou4RtvQI/discussion

EDIT: see #32 (comment).

Note: from my tests the file extension and the media type don't matter (at least, not in Chrome)