generate docs for feature gated items (#1332)

* generate docs for feature-gated items on crates.io

* add newline in Cargo.toml

* unify newlines

* fix clippy

* introduce macros for features

* commit missing file

* Update subxt/src/lib.rs

* make it compile

signer/src/lib.rs

@@ -13,16 +13,20 @@
 //! Enable the `subxt` feature to enable use of this [`sr25519::Keypair`] in signing
 //! subxt transactions for chains supporting sr25519 signatures.
 
+#![cfg_attr(docsrs, feature(doc_cfg))]
+
 #[macro_use]
 mod utils;
 mod crypto;
 
 // An sr25519 key pair implementation.
 #[cfg(feature = "sr25519")]
+#[cfg_attr(docsrs, doc(cfg(feature = "sr25519")))]
 pub mod sr25519;
 
 // An ecdsa key pair implementation.
 #[cfg(feature = "ecdsa")]
+#[cfg_attr(docsrs, doc(cfg(feature = "ecdsa")))]
 pub mod ecdsa;
 
 // Re-export useful bits and pieces for generating a Pair from a phrase,

signer/src/sr25519.rs

@@ -245,6 +245,7 @@ pub mod dev {
 // Make `Keypair` usable to sign transactions in Subxt. This is optional so that
 // `subxt-signer` can be used entirely independently of Subxt.
 #[cfg(feature = "subxt")]
+#[cfg_attr(docsrs, doc(cfg(feature = "subxt")))]
 mod subxt_compat {
     use super::*;