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

revamp OggFLAC__SeekableStreamDecoder to derive from OggFLAC__StreamDecoder instead of FLAC__SeekableStreamDecoder; rewrite seek routine to do a binary search through Ogg pages, instead of the seektable-based search of FLAC__SeekableStreamDecoder

fix bug where calling FLAC__seekable_stream_decoder_set_metadata_ignore_*() to ignore STREAMINFO or SEEKTABLE would also prevent the seekable stream decoder from getting the blocks later, which it needs to be able to seek