Fixed some error handling for invalid if statements. Started if codegen.

test/else_if_after_else.ink

@@ -0,0 +1,10 @@
+vertex main :: (pos : float3 @position) -> float4 @position {
+	if 0 > 100 {
+		
+	} else {
+
+    } else if 0 > 200 {
+
+	}
+	return float4(0.0);
+}