Added unary expressions to semcheck and codegen.

test/parse/unary.golden

@@ -0,0 +1,8 @@
+(program	
+ (fun vertex vs_vs_main -> float4 (@position)
+  [(:= position float3 (@position))] 
+  (return (float4 position.x position.y position.z 1)))
+
+ (fun pixel ps_ps_main -> float4 (@target)
+  [(:= position float4 (@outposition))] 
+  (return (float4 0.5 -1 0 1))))