This is primarily a bugfix release... although there are some new features, too!

• OverlayFS now supports asynchronous overlays! Now you can have any combination of file systems in an OverlayFS. (Thanks, @bpowers!)
• Restores IE8 compatibility. We had some bugs preventing BrowserFS from working on IE8. We'll probably remove IE8 support soon, though...
• Removes debug callback wrapping. BrowserFS used to wrap every callback it received, letting our unit tests automatically determine if there are any pending asynchronous API calls. We now strip this from release builds. (Thanks, @hrj!)
• No longer calls document.write if asynchronously loaded. Previously, we unconditionally injected an IE8/IE9 VBScript function that lets us perform binary XHR in those browsers. Now, we check if the page is loaded; if so, we inject a <script> tag instead.
• Misc small bug fixes! Too many to list here!

The next release may be a bigger one. I am likely going to drop IE8 and IE9 support so we can switch over to using Uint8Array-based Buffers for a large performance gain. Since most of the users of this library are using it in Emscripten, this is unlikely to negatively impact most of you.