Double map and plain storage support, introduce macros (#93)

* Support custom clients.

* Simplify trait bounds.

* Plain and double map storage support.

* Simplify more trait bounds.

* Add proc macro.

* Add Call, Event and Store traits.

* Update proc-macros.

* Add with_system for proc-macro.

* proc-macro: test: support signature and extra fields.

* proc-macro: test: support sharing state accross steps.

* proc-macro: test: fetch state sequentially.

* Elide lifetimes.

* Add test for plain storage.

* Run rustfmt.

proc-macro/Cargo.toml

@@ -0,0 +1,33 @@
+[package]
+name = "substrate-subxt-proc-macro"
+version = "0.1.0"
+authors = ["David Craven <david@craven.ch>"]
+edition = "2018"
+autotests = false
+
+[lib]
+proc-macro = true
+
+[dependencies]
+heck = "0.3.1"
+proc-macro2 = "1.0.10"
+proc-macro-crate = "0.1.4"
+quote = "1.0.3"
+syn = "1.0.17"
+synstructure = "0.12.3"
+
+[dev-dependencies]
+async-std = { version = "1.5.0", features = ["attributes"] }
+codec = { package = "parity-scale-codec", version = "1.2", default-features = false, features = ["derive", "full"] }
+env_logger = "0.7.1"
+frame-support = "2.0.0-alpha.6"
+pretty_assertions = "0.6.1"
+sp-core = "2.0.0-alpha.6"
+sp-keyring = "2.0.0-alpha.6"
+sp-runtime = "2.0.0-alpha.6"
+substrate-subxt = { path = ".." }
+trybuild = "1.0.25"
+
+[[test]]
+name = "balances"
+path = "tests/balances.rs"