Updated usage of attributes.
Expanded preface mentioning messaging patterns.
COMETD-575 - Document explicit RPC API.
COMETD-574 - Document new parameter "maxBufferSize".
Updated version to 3.0.3.
Updated dependency to asciidoctorj 1.5.2-SNAPSHOT to fix an issue
with tagged includes.
Specifying toc level numbering and section levels numbering.