basic_parser is abstract, not CRTP (API Change):

* `basic_parser` now uses pure virtual member functions instead
  of the curiously recurring template pattern.

Actions Required:

* Change uses of the `basic_parser` type to omit the `Derived`
  template parameter

* Classes derived from `basic_parser` no longer need to friend
  the base.

* Virtual functions in the derived class may be marked `override`.

test/beast/http/parser.cpp

@@ -45,11 +45,11 @@ public:
     }
 
     template<class ConstBufferSequence,
-        bool isRequest, class Derived>
+        bool isRequest>
     static
     void
     put(ConstBufferSequence const& buffers,
-        basic_parser<isRequest, Derived>& p,
+        basic_parser<isRequest>& p,
             error_code& ec)
     {
         buffers_suffix<ConstBufferSequence> cb{buffers};