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.

This updates the copyright header to all be the same, which is
pretty much an update of where to mail request for a copy of the GPL
and the years of the MPD project. This also puts all committers under
'The Music Player Project' umbrella. These entries should go
individually in the AUTHORS file, for consistancy.

Don't hard code the "bits" parameter to 16.  Try to use the input's
sample format, if possible.

decoder_data() returns a decoder_command, no need to call
decoder_get_command() twice after decoder_command().

If an input_stream is not seekable, libaudiofile fails to play at all:

 Audio File Library: unrecognized audio file format [error 0]

Since we know in advance whether the input_stream is seekable, just
refuse to play on a non-seekable stream.

Renamed several variables and a function.

The input_stream object should only be closed by the MPD core
(i.e. decoder_thread.c / decoder_run()).  A decoder plugin which
attempts to close it will result in a segmentation fault.

Refuse to play audio formats which are not supported by MPD.

[mk: by definition, tag_new() cannot fail - removed check]

The stream_decode() and file_decode() methods returned a boolean,
indicating whether they were able to decode the song.  This is
redundant, since we already know that: if decoder_initialized() has
been called (and dc.state==DECODE), the plugin succeeded.  Change both
methods to return void.

Instead of checking the stream_types bit set, we can simply check
whether the methods stream_decode() and file_decode() are implemented.

Don't pass the "seekable" flag with every decoder_data() invocation.
Since that flag won't change within the file, it is enough to pass it
to decoder_initialized() once per file.

The strings were constant, but the pointers weren't.  C syntax is
somewhat tricky..

All decoder_plugin structs are initialized at compile time, and must
never change.

Don't return 0/-1 on success/error, but true/false.  Instead of int,
use bool for storing flags.

A decoder_flush() invocation was missing in the FLAC plugin, resulting
in casual assertion failures due to a wrong assumption about the last
chunk's audio format.  It's much easier to remove that decoder_flush()
function and make the decoder thread call ob_flush().

Call ob_clear() in decoder_command_finished() instead of implementing
that call in every decoder plugin.

These plugins are not input plugins, they are decoder plugins.  No
CamelCase in the directory name.

Don't compile the sources of disabled decoder plugins at all, and
don't attempt to register these.

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

When there are standardized headers, use these instead of the bloated
os_compat.h.

The old struct initializers are error prone and don't allow moving
elements around.  Since we are going to overhaul some of the APIs
soon, it's easier to have all implementations use C99 initializers.

Do full C99 integer type conversion in all modules which were not
touched by Eric's merged patch.

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

Getting rid of CamelCase; not having typedefs also allows us to
forward-declare the structures.

This releases several include file dependencies.  As a side effect,
"CHUNK_SIZE" isn't defined by decoder_api.h anymore, so we have to
define it directly in the plugins which need it.  It just isn't worth
it to add it to the decoder plugin API.

"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.

Provide access to seeking for the decoder plugins; they have to know
where to seek, and they need a way to tell us that seeking has failed.

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().

Another big patch which hides internal mpd APIs from decoder plugins:
decoder plugins regularly poll dc->command; expose it with a
decoder_api.h function.

Anonymous code blocks just to declare variables look ugly.  Move the
variable declarations up and disband the code block.

Similar to previous patch: eliminate one variable by using "break".
This also simplifies the code since we can remove one level of indent.

Similar to the previous patch: pass total_time instead of manipulating
dc->totalTime directly.

dc->audioFormat is set once by the decoder plugins before invoking
decoder_initialized(); hide dc->audioFormat and let the decoder pass
an AudioFormat pointer to decoder_initialized().

We are now beginning to remove direct structure accesses from the
decoder plugins.  decoder_clear() and decoder_flush() mask two very
common buffer functions.