loadProjectAsync

Starts the load and reports the outcome through callback, without holding the calling thread. A load instantiates plug-ins, and some formats do that through the host's event loop -- WebCLAP in a browser is fetched and compiled by JavaScript -- so a thread that has to keep that loop running (the browser's main thread) must use this: loadProject would wait for work that can only run once it returns. The callback may run before this returns, and on another thread. Elsewhere this is loadProject followed by the callback.