Event hooks (#1246)

Event hooks (#1246)

* Add EventHooks internal datastructure

* Add support for 'request' and 'response' event hooks

* Support Client.event_hooks property

* Handle exceptions raised by response event hooks

* Docs for event hooks

* Only support 'request' and 'response' event hooks

* Add event_hooks to top-level API

* Event hooks

* Formatting

* Formatting

* Fix up event hooks test

* Add test case to confirm that redirects/event hooks don't currently play together correctly

* Refactor test cases

* Make response.request clear in response event hooks docs

* Drop merge marker

* Request event hook runs as soon as we have an auth-constructed request