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/basic_parser.cpp

@@ -894,10 +894,10 @@ public:
         return {s.data(), s.size()};
     }
 
-    template<class ConstBufferSequence, bool isRequest, class Derived>
+    template<class ConstBufferSequence, bool isRequest>
     std::size_t
     feed(ConstBufferSequence const& buffers,
-        basic_parser<isRequest, Derived>& p, error_code& ec)
+        basic_parser<isRequest>& p, error_code& ec)
     {
         p.eager(true);
         return p.put(buffers, ec);