Refactor swapper code with traits.

Change-Id: Ia27d3a11fea86d2ac430c3455d5247cfc4891e70
diff --git a/src/swapper/swapper.rs b/src/swapper/swapper.rs
new file mode 100644
index 0000000..bf045ee
--- /dev/null
+++ b/src/swapper/swapper.rs
@@ -0,0 +1,3 @@
+pub trait Swapper {
+    fn swap<T>(a: &mut [T], b: &mut [T]);
+}