Implemented length storage of allocated memory

examples/shell/shell.q

@@ -1,3 +1,4 @@
+import io
 import mem
 import sys
 
@@ -9,8 +10,8 @@ main() {
 	info := mem.alloc(24)
 
 	loop {
-		sys.write(1, "$ ", 2)
-		n := sys.read(0, command, length)
+		io.out("$ ")
+		n := io.in(command)
 
 		if n <= 0 {
 			return