This eliminates some overhead, because the compiler doesn't need to
consider these functions throwing.

The new class Path only holds a string pointer without being
responsible for allocation/deallocation.  The FileSystem.hxx library
accepts Path arguments instead of AllocatedPath, to avoid forcing
callers to allocate another string object.

Replaces GLib's GError.

Migrate all callers to use Path directly, instead of doing the
conversion in each caller.

These fixes were mostly generated with `codespell' [0] and manually
reviewed.

[0] http://git.profusion.mobi/cgit.cgi/lucas/codespell/

sticker_delete_value() deletes only one value in a sticker, while
the old function sticker_delete() deletes all values.

sticker_find() finds stickers with the specified name.

sticker_list_values() is only used internally in sticker.c.  Remove
sticker_song_list_values() completely, it is superseded by
sticker_song_get().

The sticker struct can be used for enumerating values.  This will
replace the sticker_list_values() function.

This updates the copyright header to all be the same, which is
pretty much an update of where to mail request for a copy of the GPL
and the years of the MPD project. This also puts all committers under
'The Music Player Project' umbrella. These entries should go
individually in the AUTHORS file, for consistancy.

[mk: merged memory leak patch; fixed indentation (tabs); fixed
documentation typo]

"Stickers" are pieces of information attached to existing MPD objects
(e.g. song files, directories, albums).  Clients can create arbitrary
name/value pairs.  MPD itself does not assume any special meaning in
them.