Modifying Protocol Buffers (or Thrift, or MessagePack, or any of the free ASN.1 implementations I could find) to support length constraints was more work than writing a custom serialisation format, so I wrote a custom format.

Protocol Buffers will be used for the wire protocol. As a quick test it's now used to serialize transport details when creating an invitation.

Added support for local transport details. Each bundle contains the sender's latest transport details.

Transport details for contacts can be stored in the database (these are arbitrary key/value pairs that describe how to reach the contact using a particular transport). Moved the generic ContactId and Rating classes out of the database package of the API.

DatabaseComponent throws an exception instead of returning silently if a contact is removed during an operation involving that contact. More unit tests.

Unit tests and bugfixes for DatabaseComponent. Merged code from various unique ID classes into a common superclass.

other groups no longer affect sendability, which makes it safe to delete all
messages from a group when unsubscribing.

Changed "neighbour" to "contact" throughout (messy, but it's only going to get messier later). Also reordered some methods in DatabaseComponent impls.