Added unary expressions to semcheck and codegen.

test/unary.ink

@@ -0,0 +1,7 @@
+vertex vs_main :: (position : float3 @position) -> float4 @position {
+	   return float4(position.x, position.y, position.z, 1.0);
+}
+
+pixel ps_main :: (position : float4 @outposition) -> float4 @target {
+	  return float4(0.5, -1, 0, 1);
+}