Created an initial pluggable tokenizer with ngram support in order to allow using lunr to drive autocomplete style search boxes.


I use this library all the time, thanks for making it available. One use case we keep doing more is client side autocomplete, and have found that ngram indexing on the server -- usually ElasticSearch -- is giving us the best results. I just need that functionality client side, and in node.js, and don't care to fuss with going out of process to Elastic Search if I can avoid it. 

I tried to follow along with your style and formatting, and hopefully did so to your satisfaction.

This sets up an index level tokenizer, I didn't dive as far in as #21, as that implies field level pipelines and tokenizers -- which really then should have some extension to pipeline to 'start' with a tokenizer then stream through multiple filters in the pipeline -- or some other field object that combines a tokenizer and pipeline.