Instantiate this class given a raw block (see parse_raw).

def from_block(cls, block):
        """Instantiate this class given a raw block (see parse_raw)."""
        rseqs = cma.realign_seqs(block)
        records = (SeqRecord(Seq(rseq, extended_protein),
                    id=bseq['id'],
                    description=bseq['description'],
                    dbxrefs=bseq['dbxrefs'].values(),   # list of strings
                    annotations=dict(
                        index=bseq['index'],
                        length=bseq['length'],
                        dbxrefs=bseq['dbxrefs'],
                        phylum=bseq['phylum'],
                        taxchar=bseq['taxchar'],
                        head_seq=bseq['head_seq'],
                        tail_seq=bseq['tail_seq'],
                        head_len=bseq['head_len'],
                        tail_len=bseq['tail_len'],      # dict
                        ),
                    # ENH: annotate with conservation levels
                    # letter_annotations=bseq['x'],
                    )
                for bseq, rseq in zip(block['sequences'], rseqs))
        return cls(records,
                # CMA attributes
                # block['one'],
                block['level'],
                block['name'],
                block['params'],
                block['query_length'],
                block['query_chars'],
                )