Implement HTTP/2 and WebSocket support; remove legacy JavaScript and CSS files

- Added HTTP/2 support in src/http2.c and src/http2.h, including session management, frame handling, and response sending.
- Introduced WebSocket functionality in src/websocket.c and src/websocket.h, covering handshake, frame parsing, and message sending.
- Created a WebSocket test page (www/websocket-test.html) for client-side interaction.
- Removed outdated JavaScript (www/script.js) and CSS (www/style.css) files.

src/server_config.h

@@ -12,6 +12,8 @@ typedef struct {
     bool automatic_startup;
     char server_name[256];   
     int verbose;
+    bool enable_http2;
+    bool enable_websocket;
 } ServerConfig;
 
 int load_config(const char *filename, ServerConfig *config);