This allows automatic optional detection of Sphinx.  This will be
useful when we start building the manpages with Sphinx, which many
users may want to have.

Currently, the hardcoded URL points to a non-existent page.

Fixup after e4dad42c

This per-object Mutex replaces the global `smbclient_mutex`.

This is no longer necessary with the new API.

This is no longer necessary with the new API.

Preparing to replace `smbclient_mutex`, for finer-grained locking.

We no longer need to call smbc_init() because we don't need the compat
layer anymore.

As a side effect, the input plugin closes the SMB/CIFS connection
after closing the file.

This solves one part of
https://github.com/MusicPlayerDaemon/MPD/issues/916

release v0.21.25

This fixes compatibility with Plex DLNA.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/851

Stop bothering people about the Tidal/Qobuz plugins.

Make LogError()/FormatError() wrappers for those.  Now we can log
exceptions with a lower level.

Prepare for templated functions.

Print all nested exceptions on a single line to avoid confusion.