Fastapi

* Add Gitter chat, badge, links, etc. <a href="https://gitter.im/tiangolo/fastapi" target="_blank">https://gitter.im/tiangolo/fastapi
</a>. PR <a href="https://github.com/tiangolo/fastapi/pull/117" target="_blank">#117</a>.

* Add docs about <a href="https://fastapi.tiangolo.com/tutorial/extending-openapi/" target="_blank">Extending OpenAPI</a>. PR <a href="https://github.com/tiangolo/fastapi/pull/126" target="_blank">#126</a>.

* Make Travis run Ubuntu Xenial (newer version) and Python 3.7 instead of Python 3.7-dev. PR <a href="https://github.com/tiangolo/fastapi/pull/92" target="_blank">#92</a> by <a href="https://github.com/blueyed" target="_blank">blueyed</a>.

* Fix duplicated param variable creation. PR <a href="https://github.com/tiangolo/fastapi/pull/123" target="_blank">#123</a> by <a href="https://github.com/yihuang" target="_blank">yihuang</a>.

* Add note in <a href="https://fastapi.tiangolo.com/tutorial/response-model/" target="_blank">Response Model docs</a> about why using a function parameter instead of a function return type annotation. PR <a href="https://github.com/tiangolo/fastapi/pull/109" target="_blank">#109</a> by <a href="https://github.com/JHSaunders" target="_blank">JHSaunders</a>.

* Fix event docs (startup/shutdown) function name. PR <a href="https://github.com/tiangolo/fastapi/pull/105" target="_blank">#105</a> by <a href="https://github.com/stratosgear" target="_blank">stratosgear</a>.

* Fix OpenAPI (JSON Schema) for declarations of Python `Union` (JSON Schema `additionalProperties`). PR <a href="https://github.com/tiangolo/fastapi/pull/121" target="_blank">#121</a>.

* Update <a href="https://fastapi.tiangolo.com/tutorial/background-tasks/" target="_blank">Background Tasks</a> with a note on Celery.

* Document response models using unions and lists, updated at: <a href="https://fastapi.tiangolo.com/tutorial/extra-models/" target="_blank">Extra Models</a>. PR <a href="https://github.com/tiangolo/fastapi/pull/108" target="_blank">#108</a>.

* Add docs and tests for <a href="https://github.com/encode/databases" target="_blank">encode/databases</a>. New docs at: <a href="https://fastapi.tiangolo.com/tutorial/async-sql-databases/" target="_blank">Async SQL (Relational) Databases</a>. PR <a href="https://github.com/tiangolo/fastapi/pull/107" target="_blank">#107</a>.

* Add support for Background Tasks in *path operation functions* and dependencies. New documentation about <a href="https://fastapi.tiangolo.com/tutorial/background-tasks/" target="_blank">Background Tasks is here</a>. PR <a href="https://github.com/tiangolo/fastapi/pull/103" target="_blank">#103</a>.

* Add support for `.websocket_route()` in `APIRouter`. PR <a href="https://github.com/tiangolo/fastapi/pull/100" target="_blank">#100</a> by <a href="https://github.com/euri10" target="_blank">euri10</a>.

* New docs section about <a href="https://fastapi.tiangolo.com/tutorial/events/" target="_blank">Events: startup - shutdown</a>. PR <a href="https://github.com/tiangolo/fastapi/pull/99" target="_blank">#99</a>.

* Document receiving <a href="https://fastapi.tiangolo.com/tutorial/query-params-str-validations/#query-parameter-list-multiple-values" target="_blank">Multiple values with the same query parameter</a> and <a href="https://fastapi.tiangolo.com/tutorial/header-params/#duplicate-headers" target="_blank">Duplicate headers</a>. PR <a href="https://github.com/tiangolo/fastapi/pull/95" target="_blank">#95</a>.

* Upgrade compatible Pydantic version to `0.21.0`. PR <a href="https://github.com/tiangolo/fastapi/pull/90" target="_blank">#90</a>.

* Add documentation for: <a href="https://fastapi.tiangolo.com/tutorial/application-configuration/" target="_blank">Application Configuration</a>.

* Fix typo in docs. PR <a href="https://github.com/tiangolo/fastapi/pull/76" target="_blank">#76</a> by <a href="https://github.com/matthewhegarty" target="_blank">matthewhegarty</a>.

* Fix link in "Deployment" to "Bigger Applications".