Added swap and list swap to stdlib.

lib/std/core/builtin.c3

@@ -27,6 +27,13 @@ macro void @scope(&variable; @body) @autoimport
 	@body();
 }
 
+macro void @swap(&a, &b) @autoimport
+{
+	$typeof(a) temp = a;
+    a = b;
+    b = temp;
+}
+
 /**
  * Convert a variant type to a type, returning an failure if there is a type mismatch.
  *

lib/std/list.c3

@@ -115,6 +115,10 @@ fn void List.free(List *list)
     list.size = 0;
 }
 
+fn void List.swap(List *list, usize i, usize j)
+{
+	@swap(list.entries[i], list.entries[j]);
+}
 
 macro Type List.@item_at(List &list, usize index) @operator(elementat)
 {