beeblink-20190608-225915-eccc48f

• simplify PC interop by removing requirement for 0-byte .inf files: the BBC will now see any suitably-named file in a drive's folder, .inf file or no, though files with no .inf file won't have useful load/execution addresses
• simplify PC interop by adding support for PC volumes, allowing the BBC to access files on the server directly, with some restrictions
• add support for mounting volumes read-only
• fix some config file issues