Useful changes to EnumString

[AlexSherbinin]

1. Added support for enums that consuming strings they have parsed from.
2. Changed behaviour to derive From trait instead of TryFrom when default variant is defined(TryFrom'll be defined automatically with Infallible as error type).

Note

Maybe a breaking change, because error type of TryFrom trait is changed from ParseError to Infallible.
Enums that consuming strings was leading to compiler error, so there's no breaking change in that part

Changes usage example:

#[derive(Debug, Eq, PartialEq, EnumString)]
#[strum(serialize_all = "UPPERCASE")]
enum HttpMethod<'a> {
    Get,
    Post,
    #[strum(default)]
    Unrecognized(&'a str),
}

[Peternator7]

@AlexSherbinin, thanks for the PR! Can you revert the formatting/style changes from this PR and include only the feature updates? They're making this PR hard to review, and the git blame becomes hard to read read if it's full of formatting changes.