get rid of Clone trait for V and K wherewer possible

[Zefick]

Cloning is not required for the core functionality of micromap as well as for HashMap, and this restriction can be removed from the many implementation blocks. The Clone constraint can be added separately for functions that really need it. E.g. that's how remove_entry's declaration may look like:

pub fn remove_entry<Q: PartialEq + ?Sized>(&mut self, k: &Q) -> Option<(K, V)>
where
    K: Borrow<Q> + Clone,
    V: Clone,
{
    ...
}

It's only function in the main block that need Clone, but I believe it's possible to remove it from there too although this is not necessary.

Impl blocks like IntoIterator for &Map and Clone for Map must declare its own constraint if it needed. They actually do it anyway and there is no need to change anything there.

If K or V not deriving Clone then it will not be possible to call into_iter() and clone() but all other methods shoud work.

In fact, standard HashMap are not required Clone for into_iter() neither it to be called by reference nor by value and it is the difference between it and the micromap. IntoIterator for &HashMap returns references to its elements and IntoIterator for HashMap just comsumes a map so it's not accessible anymore.

[yegor256]

fixed