Use substrate metadata, introduce builder for client (#4)

* Export Error type

* Fix license headers

* Remove unnecessary fully qualified associated types

* Update to parity-scale-codec, handles decoding errors

* rustfmt

* Add metadata.

* Use metadata for calls.

* Refactor generics.

* Storage metadata.

* Use builders.

* Finish making generic.

* Fix merge.

* Run rustfmt.

* Fix merge.

src/error.rs

@@ -1,12 +1,12 @@
-// Copyright 2018-2019 Parity Technologies (UK) Ltd.
+// Copyright 2019 Parity Technologies (UK) Ltd.
 // This file is part of substrate-subxt.
 //
-// ink! is free software: you can redistribute it and/or modify
+// subxt is free software: you can redistribute it and/or modify
 // it under the terms of the GNU General Public License as published by
 // the Free Software Foundation, either version 3 of the License, or
 // (at your option) any later version.
 //
-// ink! is distributed in the hope that it will be useful,
+// subxt is distributed in the hope that it will be useful,
 // but WITHOUT ANY WARRANTY; without even the implied warranty of
 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 // GNU General Public License for more details.
@@ -15,11 +15,13 @@
 // along with substrate-subxt.  If not, see <http://www.gnu.org/licenses/>.
 
 use jsonrpc_core_client::RpcError;
+use parity_scale_codec::Error as CodecError;
 use std::io::Error as IoError;
 use substrate_primitives::crypto::SecretStringError;
 
 #[derive(Debug, derive_more::From)]
 pub enum Error {
+    Codec(CodecError),
     Io(IoError),
     Rpc(RpcError),
     SecretString(SecretStringError),