A new token filter: SubSequence [LUCENE-5674]

A new configurable token filter which, given a token breaks it into sub-parts and outputs consecutive sub-sequences of those sub-parts.

Useful for, for example, using during indexing to generate variations on domain names, so that "www.google.com" can be found by searching for "google.com", or "www.google.com".

Parameters:

sepRegexp: A regular expression used split incoming tokens into sub-parts.
glue: A string used to concatenate sub-parts together when creating sub-sequences.
minLen: Minimum length (in sub-parts) of output sub-sequences
maxLen: Maximum length (in sub-parts) of output sub-sequences (0 for unlimited; negative numbers for token length in sub-parts minus specified length)
anchor: Anchor.START to output only prefixes, or Anchor.END to output only suffixes, or Anchor.NONE to output any sub-sequence
withOriginal: whether to output also the original token

EDIT: now includes tests for filter and for factory.

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Migrated from [LUCENE-5674](https://issues.apache.org/jira/browse/LUCENE-5674) by Nitzan Shaked, updated Jun 01 2014
Attachments: [subseqfilter.patch](https://apache.github.io/lucene-jira-archive/attachments/LUCENE-5674/subseqfilter.patch)

Start by reviewing the attached subseqfilter.patch and the issue's stated filter parameters, then locate the existing token-filter and factory tests referenced in the issue. Verify the proposed behavior for prefixes, suffixes, arbitrary sub-sequences, length limits, separators, and original-token output; done means the filter and factory tests cover and pass those cases.

Written by the indexing model from the issue text.