consider making toString() not zero out small parts

[donhatch]

I notice that, e.g.

• Complex(1e-16, 1e-8).toString() is "1e-8i" (I expected "1e-16 + 1e-8i")
• Complex(1e-16, 1e-16).toString() is "0" (I expected "1e-16 + 1e-16i")

It looks like this behavior is intentional: if real or imaginary part is less than
Complex.EPSILON (1e-15), toString() "helpfully" ignores it.

Is this really a good idea?

In my perception, it makes toString() into a dull and less-useful instrument. For example, I wanted to add the following test cases to complex.test.js, to confirm that expm1() works properly on small inputs; it turns out that it does, but that can't be easily confirmed with these test cases, due to toString's "helpful" zeroing behavior:

{
  set: "1e-9i",
  fn: "expm1",
  expect: "-5e-19 + 1e-9i",  // fails: comes out "1e-9i" instead
},
{
  set: "1e-20i",
  fn: "expm1",
  expect: "-5e-41 + 1e-20i",  // fails: comes out "0" instead
},
{
  set: "1e-20",
  fn: "expm1",
  expect: "1e-20",  // fails: comes out "0" instead
},

On a related note (which could be made into a separate Issue if there is interest), I'm not a fan of equals() using fuzzy equality either; I find its behavior to be unmemorable and essentially never useful to me, and, conversely, there doesn't seem to be an exact equality operator, which I would find useful. It may be too late to change equals() for reasons or backwards compatibility, but perhaps an exactEquals() could be added, at least?