Ensure metadata is in sync with running node during tests (#333)

* add test-runtime crate to dynamically obtain metadata/node_runtime for tests

* cargo fmt

* Download substrate prior to cargo calls (hopefully)

* add README explaining test-runtime

* Fix CI, fmt and clippy

* more clippy

* tweak test-node readme

* fmt the clippied

* A little tidy up in build.rs

* use ureq and raw string

* Don't export unnecessary metadata

* async_std/RpcClient/bytes instead of ureq/Value/hex

* newline

* document try_from_url error unwrap

macro/src/lib.rs

@@ -39,7 +39,6 @@ struct GeneratedTypeDerives(Punctuated<syn::Path, syn::Token![,]>);
 pub fn subxt(args: TokenStream, input: TokenStream) -> TokenStream {
     let attr_args = parse_macro_input!(args as syn::AttributeArgs);
     let item_mod = parse_macro_input!(input as syn::ItemMod);
-
     let args = match RuntimeMetadataArgs::from_list(&attr_args) {
         Ok(v) => v,
         Err(e) => return TokenStream::from(e.write_errors()),