Bump spotbugs checks to rank 20

[ctubbsii]

Bump spotbugs aggressiveness to rank 20 and fix 3 new issues:

• Add missing serialVersionUID field for anonymous subclass of serializable class
• Make use of description field from test data to avoid spotbugs error about unused field (the alternative was to suppress it; I thought printing it was better, since the description is there for our convenience)
• Internal mutable type leaking through benchmark class's API

Also include trivial fixes from code review in #22:

• Simplified .equals to one line
• Use character class for matching on literal dot to avoid escape confusion with backslash