Add slice swap benchmark.

Adds a benchmark of various different ways of swapping the elements of
two slices, including several implementations in C.

Change-Id: I7ff490aefee6edfe5d7630b851278ce1fc385e8c
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..2d3c3af
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,6 @@
+/.idea/
+/target
+
+/README.html
+
+*~