Add simple take_one

[Stargateur]

Simple equivalent of anychar() unfortunately I try to make it generic over input but it's related quite difficult:

• InputIter could have a split_first but array implementation prevent fn split_first(&self) -> Option<(Self::Item, Self)> cause this require to return Self but Self is reduce by one so the returned array is not Self anymore.
• InputTake doesn't have Sized to return Self and doesn't have Item I try to add Self: InputIter but I don't know if this would require GAT to compile I didn't succeed.

Anyway, this combinator only make sense for thing that contains u8, so I guess taking a &[u8] is ok.

PS: I wonder if the implementation for array of InputTake is really useful and not just a bit limiter to what we can do with nom trait.

[Stargateur]

I having problem check doc test cause rust-lang/cargo#6424

[Stargateur]

right now I feel this is not very useful unless someone know how to make it generic.