Pdpyras

* Added new error class :class:`PDHTTPError` for strictly application-level errors (i.e. HTTP responses vs. network errors), inherits from :class:`PDClientError`
* Removed unnecessary dependencies that were hold-outs from Python 2.7 compatibility (deprecated)
* Automatically add square brackets to query parameters that are of list type if the user forgets to do so, per the requirement of using `set filters <https://developer.pagerduty.com/docs/ZG9jOjExMDI5NTU2-filtering#set-filters>`_
* Fix bug: the :attr:`PDSession.stagger_cooldown` feature added in version 3.2 only applied to network error/retry; it now applies to all forms of retrial
* Add "update" keyword argument to :attr:`APISession.persist` that updates any existing resource with the provided values

* Make timeout configurable per-session as an instance variable (based on `a suggestion in pull 48 <https://github.com/PagerDuty/pdpyras/pull/48#discussion_r529711040>`_ made by badnetmask)
* Drop support for Python 2.7
* Improve code samples formatting improvement (jackton1 / `65 <https://github.com/PagerDuty/pdpyras/pull/65>`_)
* Replace deprecated escape sequence for the double-splat operator in docstrings (ashwin153 / `68 <https://github.com/PagerDuty/pdpyras/pull/68>`_)

* Implement work-around for issue in response plays API (issue `61 <https://github.com/PagerDuty/pdpyras/issues/61>`_)

* Add new change events API client class (hunner / `56 <https://github.com/PagerDuty/pdpyras/pull/56>`_)

* Fix regression in :attr:`EventsAPISession.post`
* Use case: explicitly-defined body (``json`` keyword argument) without a ``routing_key`` parameter
* This was previously possible (before version 4.1.3) with the ``X-Routing-Key`` header (an undocumented API feature)

* Use documented method for including the routing key in the request for API V2 (addresses `53 <https://github.com/PagerDuty/pdpyras/issues/53>`_)
* Add warning for Python 2.7
* Configurable timeout: argument to ``requests.Session.request`` set in default args to backwards-compatible 5 second value that can be set at the module level (ctrlaltdel / `48 <https://github.com/PagerDuty/pdpyras/pull/48>`_)