Refactor chunked parsing (API Change):

* parser now has a callback feature for intercepting chunk headers
  and chunk bodies

* The names for basic_parser derived class callbacks have been
  refactored

* basic_parser offers an additional callback for distinguishing
  chunk body data.

Actions Required:

* Adjust signatures for required members of user-defined
  subclasses of basic_parser

* Use the new basic_parser chunk callbacks for accessing
  chunk extensions and chunk bodies.

test/http/error.cpp

@@ -41,6 +41,7 @@ public:
         check("beast.http", error::need_more);
         check("beast.http", error::unexpected_body);
         check("beast.http", error::need_buffer);
+        check("beast.http", error::end_of_chunk);
         check("beast.http", error::buffer_overflow);
         check("beast.http", error::body_limit);
         check("beast.http", error::bad_alloc);
@@ -56,6 +57,7 @@ public:
         check("beast.http", error::bad_content_length);
         check("beast.http", error::bad_transfer_encoding);
         check("beast.http", error::bad_chunk);
+        check("beast.http", error::bad_chunk_extension);
         check("beast.http", error::bad_obs_fold);
     }
 };