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/src/lib.rs

@@ -0,0 +1,39 @@
+extern crate proc_macro;
+
+mod call;
+mod event;
+mod module;
+mod store;
+mod test;
+mod utils;
+
+use proc_macro::TokenStream;
+use synstructure::{
+    decl_derive,
+    Structure,
+};
+
+#[proc_macro_attribute]
+pub fn module(args: TokenStream, input: TokenStream) -> TokenStream {
+    module::module(args.into(), input.into()).into()
+}
+
+decl_derive!([Call] => call);
+fn call(s: Structure) -> TokenStream {
+    call::call(s).into()
+}
+
+decl_derive!([Event] => event);
+fn event(s: Structure) -> TokenStream {
+    event::event(s).into()
+}
+
+decl_derive!([Store, attributes(store)] => store);
+fn store(s: Structure) -> TokenStream {
+    store::store(s).into()
+}
+
+#[proc_macro]
+pub fn subxt_test(input: TokenStream) -> TokenStream {
+    test::test(input.into()).into()
+}