Lenient parsing of not-quite-semver versions

[kornelski]

I needed to parse versions of a library that has versions such as "0.7-beta" and "1.0". Because these versions aren't strictly semver syntax, I had to fudge it a bit by appending .0 as a fallback.

It's a bit weird to ask for non-semver parsing in a semver library, but maybe it's something you'd consider (I can imagine it might be useful in other cases, such as correcting user input that is supposed to be semver, but isn't).

Interface-wise perhaps ParseError could have a field with a best-effort parsed Version object.

[KodrAus]

Hi! Don't mind me... Just linking issues.

This looks related to #128.

And if we wanted to add a field to ParseError then it would probably be good to solve #135 using a black-box structure that could expose this through a method.

[steveklabnik]

I think I'd like to keep this crate in accordance with the spec. If I did add it, I would want it to be under a different api, like _lossy or something, and at that point, it could be in a separate crate.

Thank you, but I'm not going to take PRs for this.