exporting bytebeat songs used to work, but it had been broken at some point and now crashes. ``` Uncaught (in promise) TypeError: (intermediate value).createContext is not a function realSave https://greggman.com/downloads/examples/html5bytebeat/editor/index.js:530 save https://greggman.com/downloads/examples/html5bytebeat/editor/index.js:556 showSaveDialog https://greggman.com/downloads/examples/html5bytebeat/editor/index.js:570 startSave https://greggman.com/downloads/examples/html5bytebeat/editor/index.js:483 setElemProps https://greggman.com/downloads/examples/html5bytebeat/editor/elem.js:5 createElem https://greggman.com/downloads/examples/html5bytebeat/editor/elem.js:24 main https://greggman.com/downloads/examples/html5bytebeat/editor/index.js:343 ``` calls are made to `ByteBeatNode.createContext` and `ByteBeatNode.createStack` in `index.js`. while `ByteBeatNode` exists and these functions exist inside the prototype, debugger reports that the functions are undefined at the exception site, which is unsurprising because they are instance functions being called like static functions. another call is made to `getSampleForTime` from `ByteBeatNode`, which appears to have been removed in b28f455, so this may also crash.