split access modifier parsing into own func

- revamp parsing of access modifiers so it is correct

examples/hello.v

@@ -54,3 +54,16 @@ fn main(a int) int {
 }
 
 fn (v Typ) voidfunc() {}
+
+struct Foo {
+	a int
+mut: 
+	b int
+	c int
+pub: 
+	d int
+pub mut: 
+	e int
+pub mut mut: 
+	f int
+}