Resolves #43 by using grammar to parse English number phrases.

[bethard]

I realized that I already solved this problem in my old SCFG-based time expression parser. So I extracted out just the number portion of the grammar.

@EgoLaparra: Try it out a bit, and if you think this is better than the current WordToNumber, merge the pull request.

[EgoLaparra]

If the text cannot be parsed an UnsupportedOperationException is thrown. In this case, we should return at least the original text. For example, several in in the past several months. is identified as a Number so the SCFG is called.