Fixed sb math

Some google update made the conversions show fractions (for instance, when you say "1m in ft", it'd respond "1 meter = 3.2808399 feet (3 feet 3⅜ inches)"). There was an escape sequence, \x21, in front of the fraction, and the fraction was an html entity. The escape sequence caused the JSON interpreter to throw an exception.

I've included, in this pull request, a fix for both the exception and a way to decode the html entity.