Refactor beast core, http, tests, and examples:

* Fix warnings
* Port cmake scripts to linux
* Add command line options for running test suites
* Add examples to CMakeLists
* Return std::uint64_t from writer::content_length
* basic_parser::write takes asio::const_buffer instead of pointer and size
* Turn message test back on now that it passes
* Rename to http::headers, use std::allocator, remove http_headers
* http::message::method is now a string
* Refactor to_string for ConstBufferSequence
* Remove chunk_encode from the public interface
* Initialize members for default constructed iterators
* Disallow default construction for dependent buffer sequences

Refactor http::message serialization:

* Serialization no longer creates a copy of the
  headers and modifies them
* New function prepare(), sets Connection, Transfer-Encoding,
  Content-Length based on the body attributes and caller options.
  Callers can use prepare() to have the fields set automatically,
  or they can set the fields manually.
* Use write for operator<<
* Tests for serialization

include/beast/http/write.hpp

@@ -11,7 +11,9 @@
 #include <beast/http/error.hpp>
 #include <beast/http/message.hpp>
 #include <beast/async_completion.hpp>
+#include <beast/type_check.hpp>
 #include <boost/system/error_code.hpp>
+#include <ostream>
 #include <type_traits>
 
 namespace beast {
@@ -85,6 +87,20 @@ async_write(AsyncWriteStream& stream,
     message<isRequest, Body, Headers> const& msg,
         WriteHandler&& handler);
 
+/** Serialize a message to an ostream.
+
+    The function converts the message to its HTTP/1.* serialized
+    representation and stores the result in the output stream.
+
+    @param os The ostream to write to.
+
+    @param msg The message to write.
+*/
+template<bool isRequest, class Body, class Headers>
+std::ostream&
+operator<<(std::ostream& os,
+    message<isRequest, Body, Headers> const& msg);
+
 } // http
 } // beast