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.

include/beast/http/basic_parser.hpp

@@ -19,6 +19,7 @@
 #include <boost/assert.hpp>
 #include <limits>
 #include <memory>
+#include <type_traits>
 #include <utility>
 
 namespace beast {
@@ -136,16 +137,16 @@ public:
     using is_request =
         std::integral_constant<bool, isRequest>;
 
-    /// Copy constructor (disallowed)
+    /// Destructor
+    ~basic_parser();
+
+    /// Constructor
     basic_parser(basic_parser const&) = delete;
 
-    /// Copy assignment (disallowed)
+    /// Constructor
     basic_parser& operator=(basic_parser const&) = delete;
 
-    /// Destructor
-    ~basic_parser() = default;
-
-    /// Default constructor
+    /// Constructor
     basic_parser();
 
     /** Move constructor