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/auth.rs

@@ -0,0 +1,38 @@
+// 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/>.
+
+use primitives::Address;
+use state_machine::Externalities;
+
+use error::Result;
+use executor::RustExecutor;
+
+/// Data and some sort of Authentication Data
+type DataAndAuth = (Vec<u8>, Vec<u8>);
+
+/// Authentication contract rust implementation.
+#[derive(Debug, Default)]
+pub struct Contract;
+impl Contract {
+	/// Verify authentication data.
+	///
+	/// Given Message and Authentication Data verifies it and returns:
+	/// 1. None in case it doesn't match (i.e. signature is invalid)
+	/// 2. A address who signed that Message.
+	pub fn check_auth<E: Externalities<RustExecutor>>(&self, _ext: &E, _data: DataAndAuth) -> Result<Option<Address>> {
+		unimplemented!()
+	}
+}