feat(docs): add doc_cfg for feature-specific items

Signed-off-by: vados <vados@vadosware.io>

src/lib.rs

@@ -21,6 +21,8 @@
 //!     });
 //! }
 //! ```
+//!
+//! The example above demonstrates the synchronous usage, but `tokio` and `async-std` and corresponding modules are available as well.
 
 use std::{result::Result, time::Duration};
 

src/runtime/async_std.rs

@@ -1,4 +1,5 @@
 #![cfg(feature = "async-std")]
+#![feature(doc_cfg)]
 
 use std::{error::Error, future::Future, time::Instant};
 
@@ -10,6 +11,7 @@ use crate::{AsyncSituwaition, SituwaitionError};
 use super::AsyncWaiter;
 
 #[async_trait]
+#![doc(cfg(feature = "async-std"))]
 impl<F, A, R, E> AsyncSituwaition for AsyncWaiter<F, A, R, E>
 where
     F: Future<Output = Result<R, E>> + Send,
@@ -52,6 +54,7 @@ where
 /// Returning a result (as opposed to the error) will end waiting, otherwise
 /// the function will be retried up until the default timeout (see SituwaitionOpts)
 #[allow(dead_code)]
+#![doc(cfg(feature = "async-std"))]
 pub async fn wait_for<R, E, F, G>(factory: F) -> Result<R, SituwaitionError<E>>
 where
     R: Send + Sync + 'static,

src/runtime/tokio.rs

@@ -1,4 +1,5 @@
 #![cfg(feature = "tokio")]
+#![feature(doc_cfg)]
 
 use std::{error::Error, future::Future};
 
@@ -10,6 +11,7 @@ use crate::{AsyncSituwaition, SituwaitionError};
 use super::AsyncWaiter;
 
 #[async_trait]
+#![doc(cfg(feature = "tokio"))]
 impl<F, A, R, E> AsyncSituwaition for AsyncWaiter<F, A, R, E>
 where
     F: Future<Output = Result<R, E>> + Send,
@@ -52,6 +54,7 @@ where
 /// Returning a result (as opposed to the error) will end waiting, otherwise
 /// the function will be retried up until the default timeout (see SituwaitionOpts)
 #[allow(dead_code)]
+#![doc(cfg(feature = "tokio"))]
 pub async fn wait_for<R, E, F, G>(factory: F) -> Result<R, SituwaitionError<E>>
 where
     R: Send + Sync + 'static,