Should the constructor accept String versions of Infinity and NaN?

[jessealama]

Non-finite values should always be represented as Number values, never strings.

We'll need to discuss separately whether new Amount('Infinity') should throw, or end up with .value: Infinity.

Originally posted by @eemeli in #104 (comment)

[jessealama]

As it stands, the constructor converts "Infinity", "+Infinity", "-Infinity", and "NaN" to their Number counterparts.

[ljharb]

That seems like the proper thing to do.