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

subxt/src/tx/mod.rs

@@ -9,6 +9,8 @@
 //! additional and signed extra parameters are used when constructing an extrinsic, and is a part
 //! of the chain configuration (see [`crate::config::Config`]).
 
+use crate::macros::cfg_substrate_compat;
+
 mod signer;
 mod tx_client;
 mod tx_payload;
@@ -16,8 +18,9 @@ mod tx_progress;
 
 // The PairSigner impl currently relies on Substrate bits and pieces, so make it an optional
 // feature if we want to avoid needing sp_core and sp_runtime.
-#[cfg(feature = "substrate-compat")]
-pub use self::signer::PairSigner;
+cfg_substrate_compat! {
+    pub use self::signer::PairSigner;
+}
 
 pub use self::{
     signer::Signer,

subxt/src/tx/signer.rs

@@ -5,6 +5,7 @@
 //! A library to **sub**mit e**xt**rinsics to a
 //! [substrate](https://github.com/paritytech/substrate) node via RPC.
 
+use crate::macros::cfg_substrate_compat;
 use crate::Config;
 
 /// Signing transactions requires a [`Signer`]. This is responsible for
@@ -24,8 +25,9 @@ pub trait Signer<T: Config> {
     fn sign(&self, signer_payload: &[u8]) -> T::Signature;
 }
 
-#[cfg(feature = "substrate-compat")]
-pub use pair_signer::PairSigner;
+cfg_substrate_compat! {
+    pub use pair_signer::PairSigner;
+}
 
 // A signer suitable for substrate based chains. This provides compatibility with Substrate
 // packages like sp_keyring and such, and so relies on sp_core and sp_runtime to be included.