Fixes BufferSource - #106

• Makes node-speaker an optional dependency. npm will still install it by default, but won't error out if it fails to install. See #96.
• Ignores errors while probing so that it will try the next format instead of stopping

First release with the new build system using browserify. The attached files include Aurora.js built for the browser. You can include it along with any codecs you would like to use on your HTML page, or in an AMD build system like require.js.