Split on hyphens as well as whitespace

Example:

    Take the New York-San Francisco flight.

"york-san" isn't a word, so it shouldn't be output by the tokenizer.

For precedence, [Lucene's standard tokenizer also splits on hyphens](https://lucene.apache.org/core/3_0_3/api/core/org/apache/lucene/analysis/standard/StandardTokenizer.html), although it doesn't do it for product numbers like 31-5-6, which is not implemented here due to complexity.

Prompted by https://github.com/nolanlawson/pouchdb-quick-search/issues/3.