Add `LsInfo` method for mpd's `lsinfo` command.

MPD's `lsinfo` returns both directories & files for the given uri path
string. Files are returned with other known attributes (such as
last-modified, and ID3 tags). Directories are returned without
additional attributes.

This method matches the above behaviour, returning both files with
their attributes, and directories.

See http://www.musicpd.org/doc/protocol/database.html#command_lsinfo