Changed byte units to use binary prefixes

This PR is in response to the conversation in #37, and #95.

Numeral-js currently implements [binary bytes](https://en.wikipedia.org/wiki/Binary_prefix) (powers of 1024) but incorrectly labels them as deicmal bytes (powers of 1000).

I simply corrected the labels in the library and tests.

A more complete patch would be to implement both decimal and binary prefixes for bytes. Something I would be willing to implement.

I apologize for my editor removing whitespace.

Thank you for such a sorely-needed library! Cheers :beers:!