This filter constructs n-grams (token combinations up to a fixed size, sometimes
called "shingles") from a token stream.
The filter sets start offsets, end offsets and position increments, so
highlighting and phrase queries should work.
Position increments > 1 in the input stream are replaced by filler tokens
(tokens with termText "_" and endOffset - startOffset = 0) in the output
n-grams. (Position increments > 1 in the input stream are usually caused by
removing some tokens, eg. stopwords, from a stream.)
The filter uses CircularFifoBuffer and UnboundedFifoBuffer from Apache
Filter, test case and an analyzer are attached.