* Added ``TokenObtainSerializer.get_token`` method to facilitate customization
of token claims.
* Added ``TokenVerifyView`` to allow verification of HMAC-signed tokens by API
users who have no access to the signing key.
* Renamed ``AUTH_HEADER_TYPE`` setting to ``AUTH_HEADER_TYPES``. This setting
now contains either a single valid auth header type or a list or tuple of
valid auth header types. If authentication fails, and more than one string is
present in this tuple or list, the first item in the list will be used to
build the "WWW-Authenticate" header in the response.