Refactor (#7)

* Increment nonce when submitting transaction.

* Refactor.

* use default values from metadata
* use functions from metadata

* Nonce fixup

* Add docs.

* Add contracts module.

* Add set_code.

* Add events to metadata.

* Support pretty printing metadata.

* Add subscriptions.

* Add submit_and_watch to XtBuilder.

* nits from review

src/codec.rs

@@ -0,0 +1,19 @@
+use parity_scale_codec::{
+    Encode,
+    EncodeAsRef,
+    HasCompact,
+};
+
+pub struct Encoded(pub Vec<u8>);
+
+impl Encode for Encoded {
+    fn encode(&self) -> Vec<u8> {
+        self.0.to_owned()
+    }
+}
+
+pub fn compact<T: HasCompact>(t: T) -> Encoded {
+    let encodable: <<T as HasCompact>::Type as EncodeAsRef<'_, T>>::RefType =
+        From::from(&t);
+    Encoded(encodable.encode())
+}