The "opusinfo" program complained about preskip value that was too
small.  This commit uses OPUS_GET_LOOKAHEAD to obtain the number of
frames that shall be silence at the beginning.

Improves quality by not squeezing 32 bit samples down to 16 bit, and
then back to 32 bit floating point.  Reduces CPU usage by skipping a
conversion step.

If there are multiple pages, the last partial page must be flushed.

Eliminate the evil goto.

This is necessary for Ogg packets that span more than one page.

We can only check for negative values if the variable is signed.

Make sure the file header gets written at the beginning, before
_write() gets called.

Move the raw buffer to struct shout_data.

Make it a local variable instead.

main.c has been renamed to Main.cxx.

Implements Mantis ticket 0003340.