Introduce io module.

The rust-bitcoin upgrade will introduce `bitcoin::io` module, which
will be missing a necessary subset of traits.

To accommodate those traits' future implementations, we move the
`lightning::io` module to its own file, where we will be able to
implement the missing trait subset in the next commit.

Author: arik-so

lightning/src/io/mod.rs

@@ -0,0 +1,6 @@
+#[cfg(not(feature = "std"))]
+/// Re-export of either `core2::io` or `std::io`, depending on the `std` feature flag.
+pub use core2::io::*;
+#[cfg(feature = "std")]
+/// Re-export of either `core2::io` or `std::io`, depending on the `std` feature flag.
+pub use std::io::*;

lightning/src/lib.rs

@@ -88,12 +88,8 @@ pub mod events;
 
 pub(crate) mod crypto;
 
-#[cfg(feature = "std")]
-/// Re-export of either `core2::io` or `std::io`, depending on the `std` feature flag.
-pub use std::io;
-#[cfg(not(feature = "std"))]
-/// Re-export of either `core2::io` or `std::io`, depending on the `std` feature flag.
-pub use core2::io;
+/// Extension of the bitcoin::io module
+pub mod io;
 
 #[cfg(not(feature = "std"))]
 #[doc(hidden)]