Add support for language-specific abbreviations, and update Japanese with traditional abbreviations

Several languages don't use the thousands-millions-billions-* abbreviation paradigm (or it feels extremely weird to use it).
e.g. Japanese traditionally prefers thousands, ten thousands, million, hundred million, etc.[1]

This PR adds support for specifying a language's abbreviations along with the corresponding limits they are valid for. This does not break BC, and existing languages specs (and new languages specs that use the older format for specifying abbreviations) should continue to work as per usual.

The Japanese language spec has been updated as an example.

[1]: http://www.omniglot.com/language/numbers/japanese.htm
https://en.wikipedia.org/wiki/Japanese_numerals