Proposal creation and evaluation to plug into BFT (#77)

* reshuffle consensus libraries

* polkadot-useful type definitions for statement table

* begin BftService

* primary selection logic

* bft service implementation without I/O

* extract out `BlockImport` trait

* allow bft primitives to compile on wasm

* Block builder (substrate)

* take polkadot-consensus down to the core.

* test for preemption

* fix test build

* Fix wasm build

* Bulid on any block

* Test for block builder.

* Block import tests for client.

* Tidy ups

* clean up block builder instantiation

* justification verification logic

* JustifiedHeader and import

* Propert block generation for tests

* network and tablerouter trait

* use statement import to drive creation of further statements

* Fixed rpc tests

* custom error type for consensus

* create proposer

* asynchronous proposal evaluation

* inherent transactions in polkadot runtime

* fix tests to match real polkadot block constraints

* implicitly generate inherent functions

* add inherent transaction functionality to block body

* block builder logic for polkadot

* some tests for the polkadot API

polkadot/consensus/src/error.rs

@@ -0,0 +1,51 @@
+// 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/>.
+
+//! Errors that can occur during the consensus process.
+
+use primitives::block::HeaderHash;
+
+error_chain! {
+	links {
+		PolkadotApi(::polkadot_api::Error, ::polkadot_api::ErrorKind);
+		Bft(::bft::Error, ::bft::ErrorKind);
+	}
+
+	errors {
+		InvalidDutyRosterLength(expected: usize, got: usize) {
+			description("Duty Roster had invalid length"),
+			display("Invalid duty roster length: expected {}, got {}", expected, got),
+		}
+		ProposalNotForPolkadot {
+			description("Proposal provided not a Polkadot block."),
+			display("Proposal provided not a Polkadot block."),
+		}
+		TimestampInFuture {
+			description("Proposal had timestamp too far in the future."),
+			display("Proposal had timestamp too far in the future."),
+		}
+		WrongParentHash(expected: HeaderHash, got: HeaderHash) {
+			description("Proposal had wrong parent hash."),
+			display("Proposal had wrong parent hash. Expected {:?}, got {:?}", expected, got),
+		}
+	}
+}
+
+impl From<::bft::InputStreamConcluded> for Error {
+	fn from(err: ::bft::InputStreamConcluded) -> Self {
+		::bft::Error::from(err).into()
+	}
+}