Auto merge of #15 - chris-morgan:impl-fromiterator-for-tendril, r=SimonSapin
Auto merge of #15 - chris-morgan:impl-fromiterator-for-tendril, r=SimonSapin

Add FromIterator and Extend implementations

`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 https://github.com/rust-lang/rfcs/pull/839 for justification);
- `&str` for `StrTendril`;
- `&[u8]` for `ByteTendril`;
- `&Tendril<F>` for `Tendril<F>` (the `Extend` implementation already existed; the `FromIterator` is added).

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alexcrichton/tendril,alexcrichton/tendril,alexcrichton/tendril