Add list events method for Charge

[som-m]

Summary

• Add a new method to fetch all events belonging to a charge (Omise doc)
• Add test

QA

You should be able to fetch a list of events belonging to a given charge.

1. Retrieve a charge
   charge = omise.Charge.retrieve("chrg_test_5mozta4qq7c8rt2doub")

2. List all events of the charge
   events = charge.list_events()
events = list(events)