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.

Unified function for converting an audio_format object to a string,
for log messages and for the "status" command.

After we've been hit by Large File Support problems several times in
the past week (which only occur on 32 bit platforms, which I don't
have), this is yet another attempt to fix the issue.

An asterisk means that this attribute should not be enforced, and
stays whatever it used to be.  This way, some configuration values
work like masks.

Don't call g_error(), which will abort the process and dump core.

This patch does not affect all the config_get_X() functions.  These
need some more refactoring.

It makes no difference right now, but we're about to add an endianness
flag and will want to make sure it's correctly initialised every time.

Added public methods to get and set the current volume.