Support for number ranges

[Ztry8]

What do you think about ranges like std::ops::Range in RON?
For example:

(
  value: 0..5,
  foo: -5..=2,
)

I think it might be just syntactic sugar and a replacement for:

(
  value: (
    start: 0,
    end: 5,
  ),
  foo: (
    start: -5,
    end: 2,
  ),
)

What about floats, it may be difficult and unreadable to parse due to dots:

(
    a: 0.0..0.5,
)

[juntyr]

Syntax-wise, I see how this could be very neat. Since RON is currently tied to serde's model, and we'd want these ranges to deserialise into the range types (also once Rust switches to the new https://doc.rust-lang.org/core/range/index.html types), we'd have to make sure that the desugaring is correct, i.e. that we use the correct start, end, last names that the types expect.

[juntyr]

Feel free to open a PR that implements the feature:

• parsing support (one issue would be that we'd need to look ahead to see that a: 0..5 is not a: 0)
• a deserializer proxy that translates this into a serde mapping with the right field names
• serialising support that could look for the range types and translate them back into syntactic sugar

[Ztry8]

Thanks! I have already started working on this