Added mg_mmap and mg_munmap utility functions for memory mapping files

mongoose.h

@@ -135,6 +135,8 @@ int mg_url_encode(const char *src, size_t s_len, char *dst, size_t dst_len);
 int mg_url_decode(const char *src, int src_len, char *dst, int dst_len, int);
 int mg_terminate_ssl(struct mg_connection *c, const char *cert);
 int mg_forward(struct mg_connection *, const char *host, int port, int use_ssl);
+void *mg_mmap(FILE *fp, size_t size);
+void mg_munmap(void *p, size_t size);
 
 
 // Templates support