Refactor swapper code with traits.

Change-Id: Ia27d3a11fea86d2ac430c3455d5247cfc4891e70
diff --git a/src/swapper/mod.rs b/src/swapper/mod.rs
new file mode 100644
index 0000000..47caa9b
--- /dev/null
+++ b/src/swapper/mod.rs
@@ -0,0 +1,7 @@
+mod c_swap;
+mod rust_swap;
+mod swapper;
+
+pub use c_swap::*;
+pub use rust_swap::*;
+pub use swapper::*;