emu: SHL/SHR/SAR opcodes (BARELY TESTED!), const Op Directive

Carry Flag as yet untested and likely to contain bugs

src/emu/flags.rs

@@ -70,6 +70,7 @@ impl Flags {
       FlagOp::Eager => { self.res & 1 << OF_BIT != 0 },
       FlagOp::DEC => { self.res == self.sign_bit_mask - 1 },
       FlagOp::INC => { self.res == self.sign_bit_mask },
+      FlagOp::SHIFT => { 0 != self.sign_bit_mask & (self.dst ^ self.res) },
       FlagOp::SUB => { 0 != self.sign_bit_mask &  // In the (maybe) sign bit...
                        (self.src ^ self.dst) &    // ...operands have different signs...
                        (self.dst ^ self.res)      /* ...and result sign-bit changed */ },
@@ -93,6 +94,7 @@ pub enum FlagOp {
   Eager,  // precomputed into result, for e.g. POPF? (Anything else?)
   DEC,
   INC,
+  SHIFT,
   SUB,
 }