add a context creation benchmark

benches/context_new.rs

@@ -0,0 +1,22 @@
+#![feature(test)]
+extern crate test;
+extern crate lwkt;
+use lwkt::Context;
+
+static mut ctx_slot: *mut Context = 0 as *mut Context;
+
+#[bench]
+fn context_new(b: &mut test::Bencher) {
+  b.iter(|| unsafe {
+    let mut ctx = Context::new(move || {
+      let ctx_ptr = ctx_slot;
+      loop {
+        (*ctx_ptr).swap()
+      }
+    });
+
+    ctx_slot = &mut ctx;
+
+    ctx.swap();
+  })
+}