Only _WIN32 is defined by the compiler, and WIN32 is not standardized
and may be missing.

Closes #169

Workaround for #146.

Our IcuCaseFold() fallback using strxfrm() is not actually case
insensitive.  This commit fixes the problem by switching to
strcasecmp().  That function is not guaranteed to support UTF-8, but
it's the best we can do in this sparse situation.

Closes #111

The libsidplayfp fork has merged libsidutils into the main library.
The libsidutils we used to link with was part of the original
libsidplay project.

The user unit omits the "ProtectKernelModules" setting which fails
with modular kernels:

 Failed at step CAPABILITIES spawning /usr/bin/mpd: Operation not permitted

It is unfortunate that systemd (version 232) is unable to reduce its
own capabilities, because this requires us to split system and user
units.

 https://bugs.musicpd.org/view.php?id=4608

https://bugs.musicpd.org/view.php?id=4558

The comment about requiring libtool from 7 years ago is obsolete these
days.

Remove our own songlength database parser.

The latter doesn't exist, and this broke Vorbis-only builds.

Use libvorbis instead of libvorbisfile, which gives us more control
over the decoding process.

Will be needed to compile libxiph.a.