Update fields.md

obj.__class__ will return the actual Class object, we want to serialise a string (accessed with obj.__class__.__name__)
Kickstarter note on front page
Docs for kickstarter announcement
Beef up the kickstarter announcement
Typo
Phrasing tweak
Kickstarter announcement
Change positioning of announcement.
Update README.md
Update README.md
Update README.md
Update README.md
Add link to drf-extra-fields. Closes #1698
Merge branch 'master' of https://github.com/tomchristie/django-rest-framework
Merge pull request #1692 from davbo/patch-1

Update fields.md