TODO

1. Annotations! This is the big missing feature at this point. We need
to be able to represent complex annotations, or features, on
sequences. This is tricky as we want to be able to, for example, model
various biological entities such as chromsomes, along with conceptual
entities such as genes and and representational entities such as
sequences.

Example 1: A protein annotated with functional domains

Example 2: A gene with multiple sequences

Example 3: An annotated piece of genomic sequence

Example 4: A multiple sequence alignment

Should annotations be nested? Do annotations get their own coordinate
system or do the use the coordinate system of the underlying sequence?

2. Unify bio-align:alignment and bio:alignment

3. Support reverse-complement for RNA sequences

4. Test suite for alignments