Add options for recs-tofasta controlling sequence formatting

The split/join solution for --oneline reads clearer to me than

    $fasta =~ s/(\n.*)\n/$1/
        while $fasta =~ /\n.*\n/;

If split/join ever turns out to be a bottleneck, maybe the regex/while
above is faster.  I'm not going to benchmark it now.

While setting --width to '*' works (yay, pack templates), it also
produces "not numeric" warnings from inside Bio::SeqIO::fasta.
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