add std_instead_of_core and std_instead_of_alloc for clippy

Cargo.toml

@@ -27,3 +27,7 @@ harness = false
 [[bench]]
 name = "datetime_parse"
 harness = false
+
+[lints.clippy]
+std_instead_of_core = "warn"
+std_instead_of_alloc = "warn"

src/date.rs

@@ -1,7 +1,8 @@
-use std::error::Error as StdError;
-use std::fmt;
-use std::str;
-use std::time::{Duration, SystemTime, UNIX_EPOCH};
+use core::error::Error as CoreError;
+use core::fmt;
+use core::str;
+use core::time::Duration;
+use std::time::{SystemTime, UNIX_EPOCH};
 
 #[cfg(all(
     target_pointer_width = "32",
@@ -36,7 +37,7 @@ pub enum Error {
     InvalidFormat,
 }
 
-impl StdError for Error {}
+impl CoreError for Error {}
 
 impl fmt::Display for Error {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {

src/duration.rs

@@ -1,7 +1,7 @@
-use std::error::Error as StdError;
-use std::fmt;
-use std::str::Chars;
-use std::time::Duration;
+use core::error::Error as CoreError;
+use core::fmt;
+use core::str::Chars;
+use core::time::Duration;
 
 /// Error parsing human-friendly duration
 #[derive(Debug, PartialEq, Clone)]
@@ -48,7 +48,7 @@ pub enum Error {
     Empty,
 }
 
-impl StdError for Error {}
+impl CoreError for Error {}
 
 impl fmt::Display for Error {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {

src/wrapper.rs

@@ -1,7 +1,8 @@
-use std::fmt;
-use std::ops::Deref;
-use std::str::FromStr;
-use std::time::{Duration as StdDuration, SystemTime};
+use core::fmt;
+use core::ops::Deref;
+use core::str::FromStr;
+use core::time::Duration as StdDuration;
+use std::time::SystemTime;
 
 use crate::date::{self, format_rfc3339, parse_rfc3339_weak};
 use crate::duration::{self, format_duration, parse_duration};