add not pseudo-instruction

asm/src/main.rs

@@ -575,6 +575,10 @@ fn process_line(prgm: &mut Program, (linenum, line): (usize, String), rgx: &Rege
             chk(0);
             Instruction::Add(Reg(0), Reg(0), Labeli17::Value(0))
         }
+        "not" => {
+            chk(2);
+            Instruction::Xor(reg(0), reg(1), Op2::Direct(-1))
+        }
         "let" => {
             chk(2);
             let r = reg(0);