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`.

include/boost/beast/http/impl/parser.hpp

@@ -42,7 +42,7 @@ parser<isRequest, Body, Allocator>::
 parser(
     parser<isRequest, OtherBody, Allocator>&& other,
     Args&&... args)
-    : base_type(std::move(other))
+    : basic_parser<isRequest>(std::move(other))
     , m_(other.release(), std::forward<Args>(args)...)
     , rd_(m_.base(), m_.body())
 {