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/validator_set.rs

@@ -0,0 +1,31 @@
+// 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;
+
+/// Harcoded validator set contract.
+#[derive(Debug, Default)]
+pub struct Contract;
+impl Contract {
+	/// Returns current validator set.
+	pub fn validator_set<E: Externalities<RustExecutor>>(&self, _db: &E, _data: ()) -> Result<Vec<Address>> {
+		unimplemented!()
+	}
+}