change stored size (8/16 bit); allocate img for server in shared memory (TODO: add to client ability of reading from shm)

server.h

@@ -40,6 +40,8 @@ char *makeabspath(const char *path, int shouldbe);
 // get image size in pixels
 #define CMD_IMWIDTH     "imwidth"
 #define CMD_IMHEIGHT    "imheight"
+// get shared memory key
+#define CMD_SHMEMKEY    "shmemkey"
 
 // CCD/CMOS
 #define CMD_CAMLIST     "camlist"