Mongoose 7.3

• Improved SSI file serving: added Content-Type header
• Improved compiler compatibility, using traditional header guards instead of #pragma one
• When listening on port 0, exposing the actual port
• Disabled SSL 1.1 for OpenSSL
• Fixed C++ mg_str constructor shadowing
• Using FD_CLOEXEC on opened sockets on UNIX-like systems
• Support for new mbedtls 3.x
• Improved C++ interop with #ifdef __cplusplus
• Improved MQTT API: added qos and retain params to mg_mqtt_{pub,sub}
• Optimised RAM usage - mg_iobuf_append()
• Added MG_ARCH_FREERTOS_LWIP
• Added stm32f7 example with FreeRTOS+TCP stack
• Re-enabled Range header support (partial downloads)
• Multiple documentation fixes
• Improved mg_random() for Espressif builds
• Added multiple unit tests
• Added an ability to load mbedTLS certs from memory
• Added multipart form upload