Merge pull request RustPython#615 from adrian17/float

Migrate PyFloat to new method style

Author: OddCoincidence

vm/src/function.rs

@@ -22,6 +22,7 @@ use crate::vm::VirtualMachine;
 /// A `PyRef<T>` can be directly returned from a built-in function to handle
 /// situations (such as when implementing in-place methods such as `__iadd__`)
 /// where a reference to the same object must be returned.
+#[derive(Clone)]
 pub struct PyRef<T> {
     // invariant: this obj must always have payload of type T
     obj: PyObjectRef,