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

examples/http_server.cpp

@@ -17,9 +17,9 @@
 */
 //==============================================================================
 
-#include "http_async_server.h"
-#include "http_sync_server.h"
-#include "sig_wait.h"
+#include "http_async_server.hpp"
+#include "http_sync_server.hpp"
+#include "sig_wait.hpp"
 
 #include <boost/program_options.hpp>