WebSocket refactoring and tests:

websocket:

* Move echo server to test/
* Fix warnings
* Fix maskgen being uncopyable
* Simplify utf8_checker special member declarations
* Fix stream move assignable when owning the next layer
* Add javadocs for stream special members
* Add stream unit tests
* Move throwing member definitions to the .ipp file
* Use get_lowest_layer in stream declaration
* Perform type checks at each call site instead of constructor
* Demote close_code to a non-class enum:
    Otherwise, application specific close codes
    cannot be assigned without using static_cast.

core:

* Add streambuf_readstream special members tests
* Add move assignment operator to streambuf_readstream
* Add detail/get_lowest_layer trait
* Add static_string tests
* Move static_string from websocket to core

test/static_string.cpp

@@ -0,0 +1,191 @@
+//
+// Copyright (c) 2013-2016 Vinnie Falco (vinnie dot falco at gmail dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+// Test that header file is self-contained.
+#include <beast/static_string.hpp>
+
+#include <beast/detail/unit_test/suite.hpp>
+
+namespace beast {
+namespace websocket {
+
+class static_string_test : public beast::detail::unit_test::suite
+{
+public:
+    void testMembers()
+    {
+        using str1 = static_string<1>;
+        using str2 = static_string<2>;
+        {
+            str1 s1;
+            expect(s1 == "");
+            expect(s1.empty());
+            expect(s1.size() == 0);
+            expect(s1.max_size() == 1);
+            expect(s1.capacity() == 1);
+            expect(s1.begin() == s1.end());
+            expect(s1.cbegin() == s1.cend());
+            expect(s1.rbegin() == s1.rend());
+            expect(s1.crbegin() == s1.crend());
+            try
+            {
+                expect(s1.at(0) == 0);
+                fail();
+            }
+            catch(std::exception const&)
+            {
+                pass();
+            }
+            expect(s1.data()[0] == 0);
+            expect(*s1.c_str() == 0);
+            expect(std::distance(s1.begin(), s1.end()) == 0);
+            expect(std::distance(s1.cbegin(), s1.cend()) == 0);
+            expect(std::distance(s1.rbegin(), s1.rend()) == 0);
+            expect(std::distance(s1.crbegin(), s1.crend()) == 0);
+            expect(s1.compare(s1) == 0);
+            expect(s1.to_string() == std::string{});
+        }
+        {
+            str1 const s1;
+            expect(s1 == "");
+            expect(s1.empty());
+            expect(s1.size() == 0);
+            expect(s1.max_size() == 1);
+            expect(s1.capacity() == 1);
+            expect(s1.begin() == s1.end());
+            expect(s1.cbegin() == s1.cend());
+            expect(s1.rbegin() == s1.rend());
+            expect(s1.crbegin() == s1.crend());
+            try
+            {
+                expect(s1.at(0) == 0);
+                fail();
+            }
+            catch(std::exception const&)
+            {
+                pass();
+            }
+            expect(s1.data()[0] == 0);
+            expect(*s1.c_str() == 0);
+            expect(std::distance(s1.begin(), s1.end()) == 0);
+            expect(std::distance(s1.cbegin(), s1.cend()) == 0);
+            expect(std::distance(s1.rbegin(), s1.rend()) == 0);
+            expect(std::distance(s1.crbegin(), s1.crend()) == 0);
+            expect(s1.compare(s1) == 0);
+            expect(s1.to_string() == std::string{});
+        }
+        {
+            str1 s1;
+            str1 s2("x");
+            expect(s2 == "x");
+            expect(s2[0] == 'x');
+            expect(s2.at(0) == 'x');
+            expect(s2.front() == 'x');
+            expect(s2.back() == 'x');
+            str1 const s3(s2);
+            expect(s3 == "x");
+            expect(s3[0] == 'x');
+            expect(s3.at(0) == 'x');
+            expect(s3.front() == 'x');
+            expect(s3.back() == 'x');
+            s2 = "y";
+            expect(s2 == "y");
+            s1 = s2;
+            expect(s1 == "y");
+            s1.clear();
+            expect(s1.empty());
+            expect(s1.size() == 0);
+        }
+        {
+            str2 s1("x");
+            str1 s2(s1);
+            expect(s2 == "x");
+            str1 s3;
+            s3 = s2;
+            expect(s3 == "x");
+            s1 = "xy";
+            expect(s1.size() == 2);
+            expect(s1[0] == 'x');
+            expect(s1[1] == 'y');
+            expect(s1.at(0) == 'x');
+            expect(s1.at(1) == 'y');
+            expect(s1.front() == 'x');
+            expect(s1.back() == 'y');
+            auto const s4 = s1;
+            expect(s4[0] == 'x');
+            expect(s4[1] == 'y');
+            expect(s4.at(0) == 'x');
+            expect(s4.at(1) == 'y');
+            expect(s4.front() == 'x');
+            expect(s4.back() == 'y');
+            try
+            {
+                s3 = s1;
+                fail();
+            }
+            catch(std::exception const&)
+            {
+                pass();
+            }
+            try
+            {
+                str1 s5(s1);
+                fail();
+            }
+            catch(std::exception const&)
+            {
+                pass();
+            }
+        }
+        {
+            str2 s1("x");
+            str2 s2("x");
+            expect(s1 == s2);
+            expect(s1 <= s2);
+            expect(s1 >= s2);
+            expect(! (s1 < s2));
+            expect(! (s1 > s2));
+            expect(! (s1 != s2));
+        }
+        {
+            str1 s1("x");
+            str2 s2("x");
+            expect(s1 == s2);
+            expect(s1 <= s2);
+            expect(s1 >= s2);
+            expect(! (s1 < s2));
+            expect(! (s1 > s2));
+            expect(! (s1 != s2));
+        }
+        {
+            str2 s("x");
+            expect(s == "x");
+            expect(s <= "x");
+            expect(s >= "x");
+            expect(! (s < "x"));
+            expect(! (s > "x"));
+            expect(! (s != "x"));
+            expect("x" == s);
+            expect("x" <= s);
+            expect("x" >= s);
+            expect(! ("x" < s));
+            expect(! ("x" > s));
+            expect(! ("x" != s));
+        }
+        pass();
+    }
+
+    void run() override
+    {
+        testMembers();
+    }
+};
+
+BEAST_DEFINE_TESTSUITE(static_string,websocket,beast);
+
+} // websocket
+} // beast