Implement From<&str> for Tendril

[nikhilshagri]

Currently, the FromStr trait is implemented for Tendril, which needs to be removed and replaced with a From<&str> impl.

[SimonSapin]

We can add From<&str> easily enough, but removing FromStr is a breaking change. Going through each dependent to increment the version number requirement is more effort than removing a useless impl is worth. But we can do it next time there’s another breaking change.

[nox]

Why should we remove FromStr?

[nikhilshagri]

I don't remember exactly, but it might have been to make the code more idiomatic.

[brightly-salty]

I'd be willing to attempt to implement this and submit a PR. I can definitely add the From<&str> impl.
To me, FromStr is idiomatic enough. I see it commonly used in parsing.