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

MPD's `lsinfo` returns directories, files & playlists for the given uri path
string. Files & playlist are returned with other known attributes (such as
last-modified, & ID3 tags). Directories are returned without additional
attributes.

This method matches the above behaviour, returning files & playlists with their
attributes, & directories without additional attributes.

See http://www.musicpd.org/doc/protocol/database.html#command_lsinfo
Rename exported method to be more consistent with others in this lib.
Merge pull request #20 from zefer/feature/add-lsinfo-command

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