Tidy up tests, build scripts, and documentation:

* Concepts split up into individual files
* Function definitions moved to .ipp files
* Add more tests to fill gaps in coverage
* Fix documentation Xsl

test/handler_concepts.cpp

@@ -0,0 +1,23 @@
+//
+// 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/handler_concepts.hpp>
+
+namespace beast {
+
+namespace {
+struct T
+{
+    void operator()(int);
+};
+}
+
+static_assert(is_CompletionHandler<T, void(int)>::value, "");
+static_assert(! is_CompletionHandler<T, void(void)>::value, "");
+
+} // beast