LUCENE-4817: Add KeywordRepeaterFilter to emit tokens twice once as keyword and once not as keyword

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1454313 13f79535-47bb-0310-9956-ffa450edef68
docs for KeywordRepeatFilter

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1454384 13f79535-47bb-0310-9956-ffa450edef68