code: def index(self, overwrite=False):
          
          if self.requires_gtf:
              self.db.connect_or_create(overwrite=overwrite)
          if self.requires_transcript_fasta:
              self.transcript_sequences.index(overwrite=overwrite)
          if self.requires_protein_fasta:
              self.protein_sequences.index(overwrite=overwrite)
docs: Assuming that all necessary data for this Genome has been downloaded,
          generate the GTF database and save efficient representation of
          FASTA sequence files.