Ported the documentation from DocBook to AsciiDoc.
Updated XSD references for <web-app> elements from 2.5 to 3.0.
Removed a couple of TODOs.
Updated references to ServerSession.deliver() (method signature change).
Updated references to BayeuxServer.createChannelIfAbsent() (method name change).
Updated references to ServerChannel.publish() (method signature change).
Implemented TODO.
Updated section on inherited services.
Reviewed the primer, updating it to CometD 3 and Jetty 9.
Updated extensions section to use the require() syntax.
Updated sections referring to server-side "logLevel" configuration
parameter, which has been removed.
Updated section on the callback-polling transport.
Updated Spring documentation.
Using section mode for admonitions.
Updated sections referring to the WebSocket transports.
CometdServlet -> CometDServlet
Added missing options="header" to table.
Added ws.cometdURLMapping parameter.
Initial take at the migration section.
Completed the migration section.