Python: augmented_assignments

[simonmandlik]

Is your feature request related to a problem? Please describe.
Currently, python queries cover only standard assignments like x = 1. Augmented assignments like x += 1 could be supported as well.

Describe the solution you'd like
Should be just a matter of adding something like

(augmented_assignment
  left: (_) @assignment.lhs
  right: (_) @assignment.inner @assignment.rhs) @assignment.outer
  left: (_) @assignment.inner)

(augmented_assignment
  left: (_) @assignment.inner)