Add FromIterator and Extend implementations

[chris-morgan]

FromIterator<T> and Extend<T> are implemented for the following values of T:

• char for StrTendril;
• u8 for ByteTendril;
• &u8 for ByteTendril, for reasons of ergonomics (see also Have collections impl Extend<&T> where T: copy rust-lang/rfcs#839 for justification);
• &str for StrTendril;
• &[u8] for ByteTendril;
• &Tendril<F> for Tendril<F> (the Extend implementation already existed; the FromIterator is added).

[SimonSapin]

Please use &[b] or &[*b] instead of ref_slice, like in #14. Other than this, looks good. (The third impl is in the spirit of rust-lang/rfcs#839.)

While you’re at it, you may want to also implement Extend and rewrite FromIterator in terms of it. (But it’e fine as is.)

[chris-morgan]

OK, updated to address feedback, including adding Extend implementations. Funny how I forgot about that—I had looked at the Extend<&Tendril<F>> implementation, noted its irrelevance to the task at hand and forgotten to ever come back to it.

It might be good to implement Extend<&str> for StrTendril and Extend<&[u8]> for ByteTendril, ideally through SliceFormat though we can’t at present do it thus generically, as well. What say you?

[SimonSapin]

std has impl<'a> Extend<&'a str> for String, so adding it for StrTendril sounds fine. It doesn’t have the bytes or slice equivalent, but I don’t know a reason not to. So go for it if the coherence rules let you.

[bors-servo]

☔ The latest upstream changes (presumably #14) made this pull request unmergeable. Please resolve the merge conflicts.

[chris-morgan]

I have rebased, updated and rendered everything consistent. Ready for merging, I believe.

[SimonSapin]

Looks great. Thanks!

[SimonSapin]

@bors-servo r+

[bors-servo]

📌 Commit 0788b2b has been approved by SimonSapin

[bors-servo]

⌛ Testing commit 0788b2b with merge 37a545d...

[bors-servo]

☀️ Test successful - travis