Reverted HashSet change. Removed package name.

An ordered collection still fulfills the requirement of being unordered.
In addition, duplicates are not forbidden in the peers list, which using
a Set would block.

No package name is defined in the spec, so I've moved them out of the
package src, regardless of how bad a practice that is.
Documentation in Thing42 updated

Thing42's documentation now matches the spec's, word for word.
Removed toString since it was never in the spec.