[1.8.x] Documented Context.get() method.
[1.8.x] Documented Context.get() method.

Backport of 4d9414098bd98aacd241827a01f6ad2dff71f113 from master

pquentin/django,h4r5h1t/django-hauthy,pquentin/django,h4r5h1t/django-hauthy,h4r5h1t/django-hauthy,h4r5h1t/django-hauthy,pquentin/django