Derivable Encode & Decode (#509)

* Derive macro for simple structs.

* Derive Encode/Decode wherever we can.

* Derive for enums.

* Support discriminant.

* Get rid of some repetition.

* Support custom indices.

* Derive codec for enums wherever possible.

* Fix no_std

* WASM rebuilt

* Avoid excessive import.

* Fix compilation.

* Address review grumbles.

polkadot/runtime/wasm/Cargo.lock

@@ -454,6 +454,7 @@ dependencies = [
  "serde 1.0.64 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 1.0.64 (registry+https://github.com/rust-lang/crates.io-index)",
  "substrate-codec 0.1.0",
+ "substrate-codec-derive 0.1.0",
  "substrate-primitives 0.1.0",
  "substrate-runtime-primitives 0.1.0",
  "substrate-runtime-std 0.1.0",
@@ -639,7 +640,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 [[package]]
 name = "rustc-hex"
 version = "2.0.0"
-source = "git+https://github.com/rphmeier/rustc-hex.git#ee2ec40b9062ac7769ccb9dc891d6dc2cc9009d7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
 name = "rustc_version"
@@ -706,6 +707,15 @@ dependencies = [
  "arrayvec 0.4.7 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "substrate-codec-derive"
+version = "0.1.0"
+dependencies = [
+ "proc-macro2 0.4.4 (registry+https://github.com/rust-lang/crates.io-index)",
+ "quote 0.6.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "syn 0.14.1 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "substrate-keyring"
 version = "0.1.0"
@@ -723,10 +733,11 @@ dependencies = [
  "byteorder 1.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "crunchy 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "fixed-hash 0.1.3 (git+https://github.com/rphmeier/primitives.git?branch=compile-for-wasm)",
- "rustc-hex 2.0.0 (git+https://github.com/rphmeier/rustc-hex.git)",
+ "rustc-hex 2.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde 1.0.64 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 1.0.64 (registry+https://github.com/rust-lang/crates.io-index)",
  "substrate-codec 0.1.0",
+ "substrate-codec-derive 0.1.0",
  "substrate-runtime-std 0.1.0",
  "twox-hash 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "uint 0.1.2 (git+https://github.com/rphmeier/primitives.git?branch=compile-for-wasm)",
@@ -781,6 +792,7 @@ dependencies = [
  "serde 1.0.64 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 1.0.64 (registry+https://github.com/rust-lang/crates.io-index)",
  "substrate-codec 0.1.0",
+ "substrate-codec-derive 0.1.0",
  "substrate-primitives 0.1.0",
  "substrate-runtime-consensus 0.1.0",
  "substrate-runtime-io 0.1.0",
@@ -831,6 +843,7 @@ dependencies = [
  "serde 1.0.64 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 1.0.64 (registry+https://github.com/rust-lang/crates.io-index)",
  "substrate-codec 0.1.0",
+ "substrate-codec-derive 0.1.0",
  "substrate-primitives 0.1.0",
  "substrate-runtime-io 0.1.0",
  "substrate-runtime-std 0.1.0",
@@ -954,6 +967,7 @@ dependencies = [
  "serde 1.0.64 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 1.0.64 (registry+https://github.com/rust-lang/crates.io-index)",
  "substrate-codec 0.1.0",
+ "substrate-codec-derive 0.1.0",
  "substrate-runtime-std 0.1.0",
  "substrate-runtime-support 0.1.0",
 ]
@@ -1206,7 +1220,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum rlp 0.2.1 (git+https://github.com/paritytech/parity.git)" = "<none>"
 "checksum rlp 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)" = "89db7f8dfdd5eb7ab3ac3ece7a07fd273a680b4b224cb231181280e8996f9f0b"
 "checksum rustc-hex 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "0ceb8ce7a5e520de349e1fa172baeba4a9e8d5ef06c47471863530bc4972ee1e"
-"checksum rustc-hex 2.0.0 (git+https://github.com/rphmeier/rustc-hex.git)" = "<none>"
+"checksum rustc-hex 2.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "d2b03280c2813907a030785570c577fb27d3deec8da4c18566751ade94de0ace"
 "checksum rustc_version 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)" = "a54aa04a10c68c1c4eacb4337fd883b435997ede17a9385784b990777686b09a"
 "checksum scopeguard 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)" = "94258f53601af11e6a49f722422f6e3425c52b06245a5cf9bc09908b174f5e27"
 "checksum semver 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)" = "1d7eb9ef2c18661902cc47e535f9bc51b78acd254da71d375c2f6720d9a40403"