Improve the behavior of find_all

find_all had the following bug:

Imagine you have the following code:

for label in find_all(Text('Label')):
    print(Link(to_right_of=label).href)

The bug was that this used the same Link for each label, producing output for links that actually were not to_right_of the label in the loop.

Furthermore, this release also changes the behavior of find_all in the following way. Say you have four buttons in a 2x2 grid:

Previously, the following code used to return two buttons:

find_all(Button("Duplicate Button"), below=Button("Duplicate Button"))

(Namely, the two buttons in the second row, because they are both under a "Duplicate Button").

Now, this only returns one button (the first button in the second row). If you want both, you can still do:

for button in find_all(Button("Duplicate Button")):
    find_all(Button("Duplicate Button", below=button))

This release is a major version bump (6.x.x) because it changes the elements returned by Helium's API and may therefore be backwards-incompatible.