BREAKING: Removed callback! and introduced clones! macro

Instead of writing

let cb = callback!(clones(mut state, read_state), move |…| …);

you can write:

let cb = Callback::new({
  clones!(mut state, read_state);
  
  move |…| …
});

BREAKING: ValueContainer has been renamed to PropContainer, and ValueContainerRef to PropContainerRef accordingly

BREAKING: Removed ContextProvider::children() method, use ContextProvider::build() instead

BREAKING: Removed Persistent trait

use_effect() and use_layout_effect() can now handle closures which return () as a noop destructor