Unify the previous 3 creation methods to a single `XmlNode::new`.
This allows supporting arbitrary `nodeType` values passed to the
`XMLNode` constructor.
Rust nightly 4/13 allows f64::parse to handle "infinity", case
insensitive. This broke cases such as `Number("Infinity")`, which
should return `NaN` in AVM1.
Additionally, Rust will now print "-0" for negative zero, when
previously it would print "0".
* Return NaN for inf cases ("inf", "-Infinity", "+INF", etc.)
* Add a test for `Number("inf")` (this was also incorrect before
the latest nightly)
* Add a special case for zero in `f64_to_string` to ensure
that -0.0 gets coerced to "0".
For more info, see:
https://github.com/rust-lang/rfcs/issues/1074