Support automatic creation of directories when preloading files.

[qlambert-pro]

The init method could parse the virtualFilename and create the necessary directories.

When giving the following as filenamesToPreload argument.

[{serverFilename: "./path/filename.wav", virtualFilename: "other/path/filename.wav"}]

The resulting file system would look like:

\
├─ other
│  ├─ path
│  │  ├─ filename.wav