Add CookieError for error handling

[spk]

see #1
Cheers

[alexcrichton]

Thanks for the PR! Could this actually be called ParseError as it's returned from Cookie::parse. Additionally could it be made into an opaque struct so it can be made extensible in the future as well?

[spk]

Glad to help, there is also percent_decode that return std::str::Utf8Error
I don't know about "opaque struct" I will look it up, thanks

[alexcrichton]

Oh sorry by "opaque struct" I mean something like:

pub struct Error {
    // ... private internals
}

vs

pub enum Error {
    // public variants
}

The difference is that with a public enum adding a variant is a breaking change, but with an opaque struct adding fields is not an API-breaking-change.

[spk]

Thanks for the explanation ! I've made some changes in 3dcbde5

[alexcrichton]

Thanks!