Added support for the BIT type

- Moved socket_connection to a separate include file.
- Clarified Stream requirements.
- Made make_error_code public.
- Updated include styles to match Boost's.
- Moved <boost/myql/mysql.hpp> to <boost/mysql.hpp> to match
conventions.
- Added support for the BIT type.

closes #13
closes #21

example/query_async_coroutinescpp20.cpp

@@ -7,8 +7,7 @@
 
 //[example_query_async_coroutinescpp20
 
-#include "boost/mysql/mysql.hpp"
-#include "boost/mysql/row.hpp"
+#include <boost/mysql.hpp>
 #include <boost/asio/io_context.hpp>
 #include <boost/system/system_error.hpp>
 #include <boost/asio/co_spawn.hpp>