AMQP-39 Add AMQP MessageBuilder

Fluent API for building messages.

Add equals() and toString() implementations for Message and MessageProperties.

JIRA: https://jira.springsource.org/browse/AMQP-39

AMQP-39 Polishing; PR Comments

Biggest change is to break out a separate MessagePropertiesBuilder.

However, the MessageBuilder uses one as a delegate so that the
fluent API can be used directly on the MessageBuilder without
having to build a separate MessageProperties first.

AMQP-39 Polishing - Use Class Hierarchy

MessageBuilderSupport (abstract) with subclasses
MessageBuilder and MessagePropertiesBuilder.

AMQP-39 Fix equals Tests

Fix Typos in Docs
AMQP-116 Add Paragraph on Tracer

JIRA: https://jira.springsource.org/browse/AMQP-116