Fixed data leak when sending static files

[The-EDev]

This PR moves the file sending logic to the connection class and adds the necessary checks for errors or the need to close the connection and delete the object.

closes #291

[crow-clang-format]

--- include/crow/http_response.h	(before formatting)
+++ include/crow/http_response.h	(after formatting)
@@ -246,6 +246,5 @@
         std::function<void()> complete_request_handler_;
         std::function<bool()> is_alive_helper_;
         static_file_info file_info;
-
     };
 } // namespace crow

[luca-schlecker]

Looking good and functions as expected. 👍

[alexeimenshikh]

Clang 13 with Libc++.
I still see memory leaks when sending static files and when sending responses larger than 1Mb. Adding one line:

            res.end();
            is_writing = false;  // <---- this line
            res.clear();
            buffers_.clear();

at the end of functions do_write_static() and do_write_general() solves the problem.

[The-EDev]

@alexeimenshikh Thanks for pointing this out, it's already been implemented in #332