Removed import of unused django.forms.widgets

Added allow_empty flag

Test for #3153

Runtests should not suppress stdout. In the context of a web app only serves to hide erronous print statements.

Form fields should use textual only value representations. Closes #3139. Closes #2416. Closes #2558.

Raise helpful error when erronously including nested data in multipart post requests with test client. Closes #2919.

Handle .choices for related fields when queryset argument is actually a mamanger instance. Closes #3145.

Ensure that realtionship fields '.choices' returns an empty dict when accessed with a read-only field. Closes #2910.

Add `get_page_size` hook to `CursorPagination`

Merge branch 'cursor-limits' of https://github.com/uploadcare/django-rest-framework into uploadcare-cursor-limits

Fixed typo in docs

Fixed typo in Miscellaneous notes of 3.0 release announcement docs

Update rest-hypermedia-hateoas.md

There was a typo under ## What REST framework doesn't provide. 

Original: What REST framework doesn't do is give you is machine readable hypermedia formats such as [HAL][hal],

Fixed: What REST framework doesn't do is give you machine readable hypermedia formats such as [HAL][hal],

Changed typo in Renderer docs of BrowsableAPIRenderer

The BrowsableAPIRenderer was misspelled with an extra 'e' letter

Fix nested serializer required=False multipart data validation bug