Obsolete class CloseSongEnumerator, which was a kludge.

This reverts commit d7d9dbd2 by
reimplementing it with the current MPD API.

3 years ago, I was wrong about the "embcue" plugin being able to
replace this one, because "embcue" reads a tag named "CUESHEET", while
this plugin reads the "CUESHEET" FLAC metablock.  There's an important
difference between those two!

The old struct config_param remains only for top-level string options.

Require the version 2 which has a more sane API.

Don't use GLib.

For free().

Let the caller decide whether to strip.  Only remove \n and \r
(end-of-line markers).

Revert to the old API before commit e9e55b08, removing unnecessary
bloat.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>