Builders for incoming and outgoing headers and batches. The protocol and serial components can now be used to serialise, sign, deserialise and verify real bundles (except for message parsing).

Protocol refactoring. Each bundle now consists of a signed header and zero or more signed batches. There is no overall signature on the bundle, since the bundle's contents may need to be processed before the entire bundle has been read. The protocol does not prevent an adversary from removing batches from a bundle, reordering batches, moving them from one bundle to another, etc. However, since each batch is signed and acknowledged independently, no such guarantees are required. Bundle IDs will go away when the retransmission mechanism is changed.

Iterators throw FormatRuntimeException if a FormatException occurs, or RuntimeException if an IO error occurs. Reduced visibility of impl classes.

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.