Cleaned up serial and protocol packages in preparation for user-defined types.

api/net/sf/briar/api/serial/Consumer.java

api/net/sf/briar/api/serial/Reader.java

api/net/sf/briar/api/serial/Tag.java

api/net/sf/briar/api/serial/Writer.java

components/net/sf/briar/protocol/BundleReaderImpl.java

components/net/sf/briar/protocol/BundleWriterImpl.java

components/net/sf/briar/protocol/CountingConsumer.java

components/net/sf/briar/protocol/DigestingConsumer.java

components/net/sf/briar/protocol/MessageEncoderImpl.java

components/net/sf/briar/protocol/MessageParserImpl.java

components/net/sf/briar/protocol/SigningConsumer.java

...ts/net/sf/briar/protocol/SigningDigestingInputStream.java

components/net/sf/briar/serial/ReaderImpl.java

components/net/sf/briar/serial/WriterImpl.java

test/build.xml

test/net/sf/briar/protocol/BundleReadWriteTest.java

test/net/sf/briar/protocol/ConsumersTest.java

test/net/sf/briar/protocol/SigningStreamTest.java

test/net/sf/briar/serial/ReaderImplTest.java

test/net/sf/briar/serial/WriterImplTest.java