Support for circular sequences

In theory, circular sequences should not contain partial genes, as genes spanning the breakpoint should appear seamlessly at both the beginning and the end of the sequence. However, Prodigal/`pyrodigal` currently do not: (1) assign the same gene ID to partial sequences at both ends of the sequence; and (2) more critically, it treats the sequence edges as independent. As a result, a partial gene can sometimes be identified at only one end.

To address this issue, I've been using [a script](https://github.com/apcamargo/reorient-circular-seq) that I wrote that iteratively changes the breakpoint to minimize gene truncation. However, this approach is obviously suboptimal and can occasionally fail (i.e. find no breakpoint that eliminates truncations), as the predicted genes may change with each breakpoint change.

Although addressing this limitation would require significant effort, it would `pyrodigal` stand out among gene prediction tools.