Enable extra warnings required by rust-lang/rust

crates/stdx/src/lib.rs

@@ -1,4 +1,7 @@
 //! Missing batteries for standard libraries.
+
+#![warn(rust_2018_idioms, unused_lifetimes, semicolon_in_expressions_from_macros)]
+
 use std::process::Command;
 use std::{cmp::Ordering, ops, time::Instant};
 use std::{io as sio, iter};