Refactor sr-api to not depend on client anymore (#4086)

* Refactor sr-api to not depend on client anymore

* Fix benches

* Apply suggestions from code review

Co-Authored-By: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

* Apply suggestions from code review

substrate/core/sr-api/proc-macro/Cargo.toml

@@ -0,0 +1,26 @@
+[package]
+name = "sr-api-proc-macro"
+version = "2.0.0"
+authors = ["Parity Technologies <admin@parity.io>"]
+edition = "2018"
+
+[lib]
+proc-macro = true
+
+[dependencies]
+quote = "1.0.2"
+syn = { version = "1.0.8", features = [ "full", "fold", "extra-traits", "visit" ] }
+proc-macro2 = "1.0.6"
+blake2-rfc = "0.2.18"
+proc-macro-crate = "0.1.4"
+
+[dev-dependencies]
+sr-api = { path = ".." }
+sr-primitives = { path = "../../sr-primitives" }
+sr-version = { path = "../../sr-version" }
+test-client = { package = "substrate-test-runtime-client", path = "../../test-runtime/client" }
+
+# Required for the doc tests
+[features]
+default = [ "std" ]
+std = []