State machine crate and rust impl of executor (#17)

* Executor.

* Rust contracts implementation.

* Add documentation and fix transfer data.

* Fix auth contract interface.

* Add some executor tests.

* Validator set contract.

substrate/contracts/src/error.rs

@@ -0,0 +1,50 @@
+// Copyright 2017 Parity Technologies (UK) Ltd.
+// This file is part of Polkadot.
+
+// Polkadot 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.
+
+// Polkadot 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.
+
+// You should have received a copy of the GNU General Public License
+// along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Rust executor possible errors.
+
+#![allow(missing_docs)]
+
+use serializer;
+use state_machine;
+
+error_chain! {
+	foreign_links {
+		InvalidData(serializer::Error);
+	}
+
+	errors {
+		/// Method is not found
+		MethodNotFound(t: String) {
+			description("method not found"),
+			display("Method not found: '{}'", t),
+		}
+
+		/// Code is invalid (expected single byte)
+		InvalidCode(c: Vec<u8>) {
+			description("invalid code"),
+			display("Invalid Code: {:?}", c),
+		}
+
+		/// Externalities have failed.
+		Externalities(e: Box<state_machine::Error>) {
+			description("externalities failure"),
+			display("Externalities error: {}", e),
+		}
+	}
+}
+
+impl state_machine::Error for Error {}