Tidy up basic_parser:

- Add const qualifiers.
- Fix parser conversion constructor not copying header_limit_ and status_ fields.
- Use default special member functions when possible.
- Zero-initialize non-class members.

Signed-off-by: Damian Jarek <damian.jarek93@gmail.com>

include/boost/beast/http/impl/basic_parser.ipp

@@ -25,20 +25,6 @@ namespace boost {
 namespace beast {
 namespace http {
 
-template<bool isRequest, class Derived>
-basic_parser<isRequest, Derived>::
-~basic_parser()
-{
-}
-
-template<bool isRequest, class Derived>
-basic_parser<isRequest, Derived>::
-basic_parser()
-    : body_limit_(
-        default_body_limit(is_request{}))
-{
-}
-
 template<bool isRequest, class Derived>
 template<class OtherDerived>
 basic_parser<isRequest, Derived>::
@@ -49,6 +35,8 @@ basic_parser(basic_parser<
     , buf_(std::move(other.buf_))
     , buf_len_(other.buf_len_)
     , skip_(other.skip_)
+    , header_limit_(other.header_limit_)
+    , status_(other.status_)
     , state_(other.state_)
     , f_(other.f_)
 {