Fixes to rfc7230:

fix #1435, fix #1438

* Example and test can be built on msvc v141 15.9.6
  using /std:c++17 and BOOST_BEAST_USE_STD_STRING_VIEW.

* changed string_view.to_string() to std:string(string_view),
  awaiting availability of Library Fundamentals TS here.

* Reactivated relevant tests to param_list. #ifdef 0 test
  exhibited same assertion failed error in debug mode.
  Now fixed in DEBUG on msvc v141 15.9.6 with
  BOOST_BEAST_USE_STD_STRING_VIEW and /std:c++17.

* Looked up http paramters (transfer-encoding, etc.)
  and changed tests as well as fixing comment to
  match specs.

test/beast/http/basic_parser.cpp

@@ -1152,7 +1152,7 @@ public:
                 "HTTP/1.1 200 OK\r\n"
                 "Transfer-Encoding: chunked\r\n"
                 "\r\n"
-                "0" + s.to_string() + "\r\n"
+                "0" + std::string(s) + "\r\n"
                 "\r\n";
             error_code ec;
             test_parser<false> p;
@@ -1169,7 +1169,7 @@ public:
                 "HTTP/1.1 200 OK\r\n"
                 "Transfer-Encoding: chunked\r\n"
                 "\r\n"
-                "0" + s.to_string() + "\r\n"
+                "0" + std::string(s) + "\r\n"
                 "\r\n";
             error_code ec;
             test_parser<false> p;

test/beast/http/chunk_encode.cpp

@@ -195,11 +195,11 @@ public:
                 std::string s;
                 for(auto const& v : ce)
                 {
-                    s.append(v.first.to_string());
+                    s.append(std::string(v.first));
                     s.push_back(',');
                     if(! v.second.empty())
                     {
-                        s.append(v.second.to_string());
+                        s.append(std::string(v.second));
                         s.push_back(',');
                     }
                 }

test/beast/http/message.cpp

@@ -205,7 +205,7 @@ public:
         bool get_keep_alive_impl(unsigned) const { return true; }
         bool has_content_length_impl() const { return false; }
         void set_method_impl(string_view) {}
-        void set_target_impl(string_view s) { target = s.to_string(); }
+        void set_target_impl(string_view s) { target = std::string(s); }
         void set_reason_impl(string_view) {}
         void set_chunked_impl(bool) {}
         void set_content_length_impl(boost::optional<std::uint64_t>) {}

test/beast/http/rfc7230.cpp

@@ -88,6 +88,9 @@ public:
         cq("\t; \t xyz=1 ; ijk=\"q\\\"t\"", ";xyz=1;ijk=q\"t");
         ce(";x;y");
 
+		ce(";chunked;a=b;i=j;gzip;windowBits=12");
+		ce(";chunked;a=b;i=j;gzip;windowBits=12;permessage-deflate");
+
         // invalid strings
         cs(";", "");
         cs(";,", "");
@@ -96,6 +99,7 @@ public:
         cq(";xy=\"\x7f", "");
         cq(";xy=\"\\", "");
         cq(";xy=\"\\\x01\"", "");
+
     }
 
     static
@@ -344,11 +348,9 @@ public:
     run()
     {
         testOptTokenList();
-#if 0
         testParamList();
         testExtList();
         testTokenList();
-#endif
     }
 };
 

test/beast/http/test_parser.hpp

@@ -94,7 +94,7 @@ public:
             fc_->fail(ec);
         else
             ec = {};
-        fields[name.to_string()] = value.to_string();
+        fields[std::string(name)] = std::string(value);
     }
 
     void

test/beast/http/write.cpp

@@ -295,7 +295,7 @@ public:
         write(ts, m, ec);
         if(ec && ec != error::end_of_stream)
             BOOST_THROW_EXCEPTION(system_error{ec});
-        return tr.str().to_string();
+        return std::string(tr.str());
     }
 
     void