Add API documentation
Support 64 bit offsets
Use InputStream for all reads

The first step to multi-player support.  Not much, just a dummy
command.

The "tagtypes" command now has several sub commands which can be used
to edit that mask.

handle_tagtypes() is also being moved to ClientCommands.cxx, because
that command will be extended to access client-specific settings.

Necessary to preserve type information.  The try/catch sequence didn't
work previously.

Stop HTTP clients from exploiting MPD via forged POST requests.

Manipulates the playback range of a queued song.

Lists files and directories.  Supports storage plugins.