Implement fmt::Debug for all structures in libstd.

Part of https://github.com/rust-lang/rust/issues/31869.

Also turn on the `missing_debug_implementations` lint at the crate
level.

src/libstd/ascii.rs

@@ -12,6 +12,7 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
+use fmt;
 use mem;
 use ops::Range;
 use iter::FusedIterator;
@@ -370,6 +371,13 @@ impl ExactSizeIterator for EscapeDefault {}
 #[unstable(feature = "fused", issue = "35602")]
 impl FusedIterator for EscapeDefault {}
 
+#[stable(feature = "std_debug", since = "1.15.0")]
+impl fmt::Debug for EscapeDefault {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.pad("EscapeDefault { .. }")
+    }
+}
+
 
 static ASCII_LOWERCASE_MAP: [u8; 256] = [
     0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,