feat: Add support for float and boolean hash keys

[MartinHowarthFlexciton]

The unreachable! code at https://github.com/rust-cli/config-rs/blob/main/src/file/format/yaml.rs#L53 is reachable, and this PR fixes it for two simple types: reals and booleans.

Prior to this change you'd get this error trying to parse the following:

thread '...' panicked at .../config-0.15.9/src/file/format/yaml.rs:53:26:
internal error: entered unreachable code

The problematic case for me turned out to be float keys:

inner_float:
    0.1: "float 0.1"
    0.2: "float 0.2"

The change in this PR follows the same pattern as already exists for Strings and Integers - just parse them as strings and leave it up to the user to work out what to do with that.

Personally I only need the Real support, so happy to remove the Boolean case if that's at all contentious.

I decided not to look into whether you can craft a hash with the other Yaml types (below) because it's such an odd use case it didn't seam realistic! That said, #547 suggests that just treating Hash as string would have avoided that users' problem. However, converting from these types back into the exact string format they were parsed in would be difficult, so it's not clear what the right implementation would be. So getting the simpler case (reals, booleans) done feels like the right sized change to make.

    Array(Array),
    Hash(Hash),
    Alias(usize),
    Null,
    BadValue,

Let me know what you think! And thanks for maintaining this useful crate :)

[epage]

Seems we should turn that panic into an error

[MartinHowarthFlexciton]

I've turned the remaining unsupported cases into a useful error message as you suggested

[coveralls]

Pull Request Test Coverage Report for Build 13814392108

Details

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.02%) to 65.403%

---

Totals
Change from base Build 13814057810:	0.02%
Covered Lines:	949
Relevant Lines:	1451

---

💛 - Coveralls