The sequence_db class: using sequence databases

The sequence_db class holds a database of sequences. Such a database is similar to a multiple sequence alignment, but contains less auxilliary information (for example, no sequence may contain gaps). This requires less memory than a true alignment, and is thus more suited for large databases of sequences. Such a database can be scanned for matches to an input sequence with sequence_db.search(), used to build sequence profiles with profile.build() or filtered by given criteria with sequence_db.filter().