Handle some semantic merge conflicts

Something that wasn't part of this PR: the work to support nested
`Option<[ChronoType]>` was merged without being adjusted for the no-std
support

And now there are some unused import warnings because they need to get
configged out.

src/datetime.rs

@@ -1141,7 +1141,7 @@ pub mod serde {
     /// # fn main() { example().unwrap(); }
     /// ```
     pub mod ts_nanoseconds_option {
-        use std::fmt;
+        use core::fmt;
         use serdelib::{ser, de};
 
         use {DateTime, Utc};
@@ -1432,7 +1432,7 @@ pub mod serde {
     /// # fn main() { example().unwrap(); }
     /// ```
     pub mod ts_milliseconds_option {
-        use std::fmt;
+        use core::fmt;
         use serdelib::{ser, de};
 
         use {DateTime, Utc};
@@ -1719,7 +1719,7 @@ pub mod serde {
     /// # fn main() { example().unwrap(); }
     /// ```
     pub mod ts_seconds_option {
-        use std::fmt;
+        use core::fmt;
         use serdelib::{ser, de};
 
         use {DateTime, Utc};

src/naive/date.rs

@@ -3,6 +3,7 @@
 
 //! ISO 8601 calendar date without timezone.
 
+#[cfg(any(feature = "alloc", feature = "std", test))]
 use core::borrow::Borrow;
 use core::{str, fmt};
 use core::ops::{Add, Sub, AddAssign, SubAssign};

src/naive/datetime.rs

@@ -3,6 +3,7 @@
 
 //! ISO 8601 date and time without timezone.
 
+#[cfg(any(feature = "alloc", feature = "std", test))]
 use core::borrow::Borrow;
 use core::{str, fmt, hash};
 use core::ops::{Add, Sub, AddAssign, SubAssign};

src/naive/time.rs

@@ -3,6 +3,7 @@
 
 //! ISO 8601 time without timezone.
 
+#[cfg(any(feature = "alloc", feature = "std", test))]
 use core::borrow::Borrow;
 use core::{str, fmt, hash};
 use core::ops::{Add, Sub, AddAssign, SubAssign};