Adding HTTPException subclasses for HTTP statuses 428, 429, and 431,
which were recently added in RFC 6585.
missed HTTP_STATUS_CODES
Remove docs reference to import_module
Merge pull request #200 from jessaustin/master

Add HTTPExceptions for 428, 429, and 431
Merge pull request #240 from vreon/patch-1

Remove docs reference to import_module