Add Hypothesis tests for TradeCodes

[CyberiaResurrection]

This PR hooks up the Hypothesis testing library, which enables property-based tests:

1. For all data matching some specification.
2. Perform some operations on the data.
3. Assert something about the result.

Starline parsing has historically been less than robust, and trade code parsing was no better than the rest of it, so this PR started there.

The specification i used was Given an otherwise-valid input string, it should parse cleanly to a well-formed TradeCodes object that then should cleanly round-trip to/from string. As could be expected, smoke poured out of TradeCode parsing. So I went thru and fixed that.

[tjoneslo]

A few comments and some suggestions for improvements.

[tjoneslo]

Let's get this merged in. I'm concerned with the _process_sophonts_and_homeworlds() being a hand-written parser and therefore fragile. But let's fix that in the next pass.