Improve documentation for <integer>::from_str_radix

[Krappa322]

Two improvements to the documentation:

• Document - as a valid character for signed integer destinations
• Make the documentation even more clear that extra whitespace and non-digit characters is invalid. Many other languages, e.g. c++, are very permissive in string to integer routines and simply try to consume as much as they can, ignoring the rest. This is trying to make the transition for developers who are used to the conversion semantics in these languages a bit easier.

[rustbot]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @scottmcm (or someone else) some time within the next two weeks.

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[Krappa322]

In case the built documentation is inconvenient to access:

[Krappa322]

And some screenshots again, for convenience:

[scottmcm]

Thanks for including the screenshot; this is looking great!

One request: can you put an example of the error case too? I think there's a bunch of people who are less likely to read the text in detail, but a assert_matches!("1 ".parse(), Err(_)); or similar test should help emphasize.

@rustbot author

[Krappa322]

Apologies for the long wait time :)

Added an error example for trailing characters. Didn't seem like there were that strong feelings on the macro syntax and I'm not really in the mood for macro development right now so I'll leave that as is if you all agree.

[Krappa322]