make --serial-number or the default random serial number apply only to the first stream, and increment it for subsequent streams

print error if output file already exists, instead of overwriting by default; add -f (--force) option to force overwriting of files

when encoding to Ogg FLAC, set a random serial number (instead of 0) if one is not provided on the command-line

add callback-based versions of chain writing: FLAC__metadata_chain_check_if_tempfile_needed(), FLAC__metadata_chain_write_with_callbacks(), FLAC__metadata_chain_write_with_callbacks_and_tempfile()

begin addition of callback-based option to metadata interfaces; start by converting chain reader to callback-based

use the OggFLAC__FileDecoder instead of the old OggFLAC__StreamDecoder way for all Ogg FLAC decoding, and enable use of --skip with Ogg FLAC