Various fixes, warnings:

* Fix sig_wait
* Fix websocket strict aliasing warning
* Fix invokable strict aliasing
* Silence fread warning in examples
* Silence integer conversion warnings
* Build parser-bench as test
* Disable unused variable warning for asio:
    Caused by static variables declared in <boost/asio/error.hpp>
    No known workaround.

include/beast/http/impl/basic_parser.ipp

@@ -42,6 +42,9 @@ write(void const* data, std::size_t size, error_code& ec)
     using beast::http::detail::to_field_char;
     using beast::http::detail::to_value_char;
     using beast::http::detail::unhex;
+ 
+    if(size == 0 && s_ != s_closed)
+        return 0;
 
     auto begin =
         reinterpret_cast<char const*>(data);
@@ -338,6 +341,7 @@ write(void const* data, std::size_t size, error_code& ec)
             if(cb(&self::call_on_reason))
                 return used();
             pos_ = 0;
+            s_ = s_res_status;
             break;
 
         case s_res_status: