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

codegen/Cargo.toml

@@ -5,14 +5,12 @@ authors.workspace = true
 edition.workspace = true
 rust-version.workspace = true
 publish = true
-
 license.workspace = true
 repository.workspace = true
 documentation = "https://docs.rs/subxt-codegen"
 homepage.workspace = true
 description = "Generate an API for interacting with a substrate node from FRAME metadata"
 
-
 [features]
 default = []
 fetch-metadata = ["dep:jsonrpsee", "dep:tokio", "dep:frame-metadata"]
@@ -38,3 +36,10 @@ getrandom = { workspace = true, optional = true }
 
 [dev-dependencies]
 scale-info = { workspace = true, features = ["bit-vec"] }
+
+[package.metadata.docs.rs]
+features = ["fetch-metadata"]
+rustdoc-args = ["--cfg", "docsrs"]
+
+[package.metadata.playground]
+defalt-features = true