[UIMA-3969] split out JSON methods from XML ones in XMLizable into new interface JSONizable. Refactor compareFeat to eliminate one method

git-svn-id: https://svn.apache.org/repos/asf/uima/uimaj/trunk@1618884 13f79535-47bb-0310-9956-ffa450edef68
[UIMA-3969] add a chapter to the UIMA reference document covering JSON serialization, and mention it in the tutorial book. 

git-svn-id: https://svn.apache.org/repos/asf/uima/uimaj/trunk@1618886 13f79535-47bb-0310-9956-ffa450edef68