[UIMA-3969] update ref docs for JSON serialization to conform to next iteration of design

git-svn-id: https://svn.apache.org/repos/asf/uima/uimaj/trunk@1623467 13f79535-47bb-0310-9956-ffa450edef68
[UIMA-4002] fix flush method to reset lastNodeGotten

git-svn-id: https://svn.apache.org/repos/asf/uima/uimaj/trunk@1623554 13f79535-47bb-0310-9956-ffa450edef68
no Jira -add clear() method to support some additional testing

git-svn-id: https://svn.apache.org/repos/asf/uima/uimaj/trunk@1623558 13f79535-47bb-0310-9956-ffa450edef68