consolidate AcceptEncodingXXXHeader classes into the single AcceptEncoding class

Author: mmerickel

docs/api/webob.txt

@@ -41,22 +41,10 @@ methods:
        acceptable_offers, best_match, quality
 
 .. autoclass:: AcceptEncoding
-   :members: parse
-
-.. autoclass:: AcceptEncodingValidHeader
-   :members: parse, header_value, parsed, __init__, __add__, __bool__,
-         __contains__, __iter__, __radd__, __repr__, __str__,
-             acceptable_offers, best_match, quality
-
-.. autoclass:: AcceptEncodingNoHeader
-   :members: parse, header_value, parsed, __init__, __add__, __bool__,
-         __contains__, __iter__, __radd__, __repr__, __str__,
-             acceptable_offers, best_match, quality
-
-.. autoclass:: AcceptEncodingInvalidHeader
-   :members: parse, header_value, parsed, __init__, __add__, __bool__,
-         __contains__, __iter__, __radd__, __repr__, __str__,
-             acceptable_offers, best_match, quality
+   :members:
+       parse, header_value, parsed, header_state, __init__, __add__,
+       __bool__, __radd__, __repr__, __str__, __contains__, copy,
+       acceptable_offers, best_match, quality
 
 .. autoclass:: AcceptLanguage
    :members: parse