Fix `ast::Number::value`

[matklad]

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https://github.com/matklad/tom/blob/5a1b98e0b0b13529a917a9c2212f6813a9eb1948/src/ast/mod.rs#L46 is just an unimplemented!() stub.

I think we should replace it with two methods: value_i64() -> Option<i64> and value_f64() -> f64, because TOML supports both floats and ints.

The tests should go here: https://github.com/matklad/tom/blob/5a1b98e0b0b13529a917a9c2212f6813a9eb1948/tests/suite/ast.rs#L26-L32

See https://github.com/matklad/tom/issues/2 as well.

[ehuss]

What do you think about keeping integers and floats as separate types? The model API will need to differentiate between them (currently it panics when it sees a float), and since Rust generally doesn't let integers/floats mix I think it would be more convenient. That may require pushing the distinction down all the way into the lexer. Was there some motivation for treating them the same?

[matklad]

Agree, it makes sense to distinguish between floats and ints in all of lexer, CST and AST.

[matklad]

As for original motivation, it’s basically a historic accident.

An interesting question is what should we do if a number overflows i64? Optoind are either to return an option or to produce an error during validation and panic in the value method.