Add ngram tokens

[vickumar1981]

• Adds ability to retrieve ngrams for a String, returning a List[String]
• Has corresponding java implementation using util.StringDistance.nGramToken(String s, Int n)

[coveralls]

Pull Request Test Coverage Report for Build 181

• 2 of 3 (66.67%) changed or added relevant lines in 3 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.7%) to 99.281%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/main/scala/com/github/vickumar1981/stringdistance/interfaces/NGramTokenizer.scala	0	1	0.0%
<!--	Total:	2	3	66.67%	-->

Files with Coverage Reduction	New Missed Lines	%
src/main/scala/com/github/vickumar1981/stringdistance/package.scala	1	96.97%
<!--	Total:	1		-->

Totals
Change from base Build 178:	-0.7%
Covered Lines:	276
Relevant Lines:	278

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💛 - Coveralls