API simplification.  We can now avoid abusing a "size_t*" as
additional return value.

Avoid GLib.

Obsolete, our logging library doesn't ues GLib anymore.

Use only ConfigData.hxx in plugin sources to reduce header
dependencies.

Replaces GLib's GError.

Deprecated.

Look up top-level config options by enum (= integer), not by name
string.

Push the new mode to the filter instead of accessing global variables
through replay_gain_get_real_mode().

Make sure we get a UTF-8 encoded string.

Declaring the global variable _CRT_fmode is a documented hack.  What
an ugly platform!

Add an option for each audio output which enables the use of the
hardware mixer, instead of the software volume code.

This is hardware specific, and assumes linear volume control.  This is
not the case for hardware mixers which were tested, making this patch
somewhat useless, but we will use it to experiment with the settings,
to find a good solution.

Apply the replay gain in the output thread.  This means a new setting
will be active instantly, without going through the whole music pipe.
And we might have different replay gain settings for each audio output
device.

Log to stderr, not to stdout (which broke PCM output).

This patch prepares support for floating point samples (and probably
other formats).  It changes the meaning of the "bits" attribute from a
bit count to a symbolic value.