cleanup and improved function tests

src/main.rs

@@ -3,6 +3,12 @@
 #![feature(stmt_expr_attributes)]
 #![feature(const_trait_impl)]
 #![feature(core_intrinsics)]
+#![feature(const_convert)]
+#![feature(const_default_impls)]
+#![feature(const_fn_floating_point_arithmetic)]
+#![feature(const_assume)]
+#![feature(const_option_ext)]
+#![feature(const_slice_index)]
 
 #[macro_use]
 extern crate static_assertions;