This replaces the attributes bits, channels, sampleRate.

The last bit of CamelCase in audio_format.h.  Additionally, rename a
bunch of local variables.

CamelCase is ugly...  rename all functions.

"bool" should be used in C99 programs for boolean values.

Again, a data type which can be forward-declared.

pause() puts the audio output into pause mode: if supported, it may
perform a special action, which keeps the device open, but does not
play anything.  Output plugins like "shout" might want to play silence
during pause, so their clients won't be disconnected.  Plugins which
do not support pausing will simply be closed, and have to be reopened
when unpaused.

This pach includes an implementation for the shout plugin, which
sends silence chunks.

There was a known deadlocking bug in the notify library: when the
other thread set notify->pending after the according check in
notify_wait(), the latter thread was deadlocked.  Resolve this by
synchronizing all accesses to notify->pending with the notify object's
mutex.  Since notify_signal_sync() was never used, we can remove it.
As a consequence, we don't need notify_enter() and notify_leave()
anymore; eliminate them, too.

Get rid of CamelCase, and don't use a typedef, so we can
forward-declare it, and unclutter the include dependencies.

Give player.c a better name, meaning that the code is used to control
the player thread.

This is the last of the three variables.  Now we don't need
playerData.h anymore in most sources.

Now that "dc" is available here, we don't have to pass it to
decoder_is_idle() and decoder_is_starting() anymore.

decode() is a trivial wrapper for decodeParent().  Merge both and
rename them to do_play().

Unfortunately, we have to pass the DecoderControl pointer to these
inline functions, because the global variable "dc" may not be
available here.  This will be fixed later.

When dc->error!=NOERROR, we do not need to check state!=START.
Simplify the checks by moving the error check to the top.

The decoder thread is responsible for resetting dc->command after a
command was executed.  As a consequence, we can assume that
dc->command is already NONE after decoder_stop().

The source "decoder_control.c" provides an API for controlling the
decoder.  This replaces various direct accesses to the DecoderControl
struct.

playerKill() was marked as deprecated, but it seems like a good idea
to do proper cleanup in all threads (e.g. for usable valgrind
results).  Introduce the command "EXIT" which makes the player thread
exit cleanly.

playerWait() stops the player thread (twice!) and closes the output
device.  It should be well enough to just send CLOSE_AUDIO, without
STOP.

This requires a tiny change to the player thread code: make it break
when CLOSE_AUDIO is sent.

To make the code more consistent, call quitDecode() only at the end of
decodeParent().

Move code which runs in the player thread to player_thread.c.  Having
a lot of player thread code in decode.c isn't easy to understand.

decode.c should be a lot smaller; start by moving all code which
handles cross-fading to crossfade.c.  Also includes camelCase
conversion.

Make the code more readable by hiding big formulas in an inline
function with a nice name.

Make calculateCrossFadeChunks() more generic and portable by
eliminating global variable access.

InputPlugin to decoder_plugin, and no camelCase.

"decoder plugin" is a better name than "input plugin", since the
plugin does not actually do the input - InputStream does.  Also don't
use typedef, so we can forward-declare it if required.

PlayerControl.command replaces the old attributes play, stop, pause,
closeAudio, lockQueue, unlockQueue, seek.  The main thread waits for
each command synchronously, so there can only be one command enabled
at a time anyway.

Some decoder commands are implemented in the decoder plugins, thus
they need to have an API call to signal that their current command has
been finished.  Let them use the new decoder_command_finished()
instead of the internal dc_command_finished().

We want to expose the AudioFormat structure to plugins; remove some
clutter by moving its declaration to a separate header file.

After the decoder has been initialized and the audio device has been
opened, don't sleep.  The decoder plugin won't do anything special nor
will it care to wake us up for some reason.

The decoder struct should later be made opaque to the decoder plugin,
because maintaining a stable struct ABI is quite difficult.  The ABI
should only consist of a small number of stable functions.

Don't use wrappers like player_wakeup_decoder_nb().  These have been
wrappers calling notify.c functions, for compatibility with the
existing code when we migrated to notify.c.

The "if" block breaked out of the loop.  That means we can move the
code out of the "else" block.

dc_command_finished() is invoked by the decoder thread when it has
finished a command (sent by the player thread).  It resets dc.command
and wakes up the player thread.  This combination was used at a lot of
places, and by introducing this function, the code will be more
readable.

Busy wait loops are a bad thing, especially when the response time can
be very long - busy waits eat a lot of CPU, and thus slow down the
other thread.  Since the other thread will notify us when it's ready,
we can use notify_wait() instead.