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

Cargo.lock

@@ -2015,7 +2015,7 @@ dependencies = [
  "http",
  "hyper",
  "log",
- "rustls 0.21.9",
+ "rustls 0.21.10",
  "rustls-native-certs 0.6.3",
  "tokio",
  "tokio-rustls 0.24.1",
@@ -2264,7 +2264,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "776d009e2f591b78c038e0d053a796f94575d66ca4e77dd84bfc5e81419e436c"
 dependencies = [
  "anyhow",
- "async-lock 3.2.0",
+ "async-lock 3.3.0",
  "async-trait",
  "beef",
  "futures-timer",
@@ -3289,7 +3289,7 @@ version = "2.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "35e4980fa29e4c4b212ffb3db068a564cbf560e51d3944b7c88bd8bf5bec64f4"
 dependencies = [
- "base64 0.21.5",
+ "base64 0.21.6",
  "rustls-pki-types",
 ]
 
@@ -4665,7 +4665,7 @@ version = "0.24.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c28327cf380ac148141087fbfb9de9d7bd4e84ab5d2c28fbc911d753de8a7081"
 dependencies = [
- "rustls 0.21.9",
+ "rustls 0.21.10",
  "tokio",
 ]