Rename struct Encoder to PreparedEncoder, and add a new (abstract)
class Encoder which represents one encoder instance.

The old struct config_param remains only for top-level string options.

The "written" argument to shine_encode_buffer() and shine_flush() was
changed from "long" to "int", which breaks API and ABI compatibility.
This is a big deal, and it doesn't seem worthwile to keep support for
the (broken) 3.0 release.

.. and move the plugins to src/encoder/plugins/.

Initializing and closing the Shine library without
writing any data results in a segmentation fault.
The current workaround writes zeroes if there was
no actual data.

Now writes to the de-interleaved buffers directly,
instead of writing to an intermediate fifo buffer.

Fix indentation and 80 char width lines.

This encoding plugin features a fixed-point mp3 encoder,
with faster encoding on architectures without a FPU.

Right now the encoder is limited to stereo and 16 bit depth.
The bitrate and sample rate can be modified in audio_output.

audio_output {
        type            "httpd"
        name            "My shine stream"
        encoder         "shine"
        port            "8000"
        format          "44100:16:2"
        bitrate         "320"  # default: 128
}