Calculator: give result for sin(pi)

Man, literal months of tweaking and improving on the previous pull request and within 10 queries of noticing the new Calculator was live.. I found a problem.

Turns out that sin(pi) isn't exactly 0 when you account for floating point issues.  This gets caught in the attempts to avoid showing floating point in exponent form.

The fix applied here is to treat anything smaller than 1e-7 as 0, unless it would otherwise be rounded (probably also to 0 but I dare not speculate.)