Configurable Config and Extra types (#373)

* WIP config

* WIP separate default config

* Separate trait impls on client

* WIP introduce new ApiConfig (to be renamed) trait

* Update generated polkadot codegen

* Allow configuring Config and Extra types independently

* Add extra default configuration

* Revert ir parsing of config attr

* Add default-features = false to substrate deps

* Revert "Add default-features = false to substrate deps"

This reverts commit 099d20cd4cbf8000ff938d1dc090ecbc28a5e788.

examples/fetch_remote.rs

@@ -14,7 +14,11 @@
 // You should have received a copy of the GNU General Public License
 // along with subxt.  If not, see <http://www.gnu.org/licenses/>.
 
-use subxt::ClientBuilder;
+use subxt::{
+    ClientBuilder,
+    DefaultConfig,
+    DefaultExtra,
+};
 
 #[subxt::subxt(runtime_metadata_path = "examples/polkadot_metadata.scale")]
 pub mod polkadot {}
@@ -27,7 +31,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
         .set_url("wss://rpc.polkadot.io:443")
         .build()
         .await?
-        .to_runtime_api::<polkadot::RuntimeApi<polkadot::DefaultConfig>>();
+        .to_runtime_api::<polkadot::RuntimeApi<DefaultConfig, DefaultExtra<DefaultConfig>>>();
 
     let block_number = 1;