Missing Javadoc

[JonathanMace]

• Package level javadoc (https://jonathanmace.github.io/tracingplane/doc/javadoc/index.html). Can just be a duplicate of the static class docs.
• Explanation of examples here: https://jonathanmace.github.io/tracingplane/doc/javadoc/edu/brown/cs/systems/baggage_buffers_examples/package-summary.html
• Good documentation of main apis in all four layers.
• Reasonable documentation of code elsewhere.