Add auto File type detection

[IJabz]

In the current release AudioFileIO uses the provided file's extension to guess which concrete AudioFile implementation should be returned to the caller.

It would be really useful having two other options: 1. one that determines the concrete AudioFile impl. to be returned based on the magic-number exposed by the file (the extension cannot be always available) 2. another API that accepts a mime-type provided by the caller, according to which the most appropriate AudioFile is provided

I require this as I'm storing audio files of various formats using a SHA-1 identifier e.g. /some/path/2f/d4/e1c67a2d28fced849ee1bb76e7391b93eb12

This is best practice approach for mass file storage to provide a form of data integrity and remove the requirement to sync database and file system upon metadata in the db being changed. That metadata contains the mime-type and original extension which I can supply the AudioFileIO method along with the File instance to allow identification of the format.