Clean up random seed to make a bit more flexible (#2456)

* Reformulate random seed to be more random

- First 80 random values come from cycling the incomplete series (
  instead of filling with zeroes)
- Calculate random material each usage (use a single amalgamated
  ring buffer to store them for avoiding 81 lookups each time)
- Mutate inputs by hashing each with:
  - its index (into the 81)
  - an additional "subject" key provided by caller

This keeps the final output low-influence while still allowing
it to be used as the seed to independent contexts. (Hashing the
result to give the final seed is no better than using parent_hash).

* Docs

* Bump runtime

* Update notes

* Remove feature(alloc)

* Update srml/system/src/lib.rs

Co-Authored-By: gavofyork <github@gavwood.com>

substrate/core/executor/wasm/src/lib.rs

@@ -1,7 +1,6 @@
 #![no_std]
 #![cfg_attr(feature = "strict", deny(warnings))]
 
-#![feature(alloc)]
 extern crate alloc;
 use alloc::vec::Vec;
 use alloc::slice;

substrate/core/finality-grandpa/primitives/src/lib.rs

@@ -17,7 +17,6 @@
 //! Primitives for GRANDPA integration, suitable for WASM compilation.
 
 #![cfg_attr(not(feature = "std"), no_std)]
-#![cfg_attr(not(feature = "std"), feature(alloc))]
 
 #[cfg(not(feature = "std"))]
 extern crate alloc;

substrate/core/primitives/src/lib.rs

@@ -19,7 +19,6 @@
 #![warn(missing_docs)]
 
 #![cfg_attr(not(feature = "std"), no_std)]
-#![cfg_attr(not(feature = "std"), feature(alloc))]
 
 /// Initialize a key-value collection from array.
 ///

substrate/core/sr-io/src/lib.rs

@@ -22,7 +22,6 @@
 #![cfg_attr(not(feature = "std"), feature(lang_items))]
 #![cfg_attr(not(feature = "std"), feature(alloc_error_handler))]
 #![cfg_attr(not(feature = "std"), feature(core_intrinsics))]
-#![cfg_attr(not(feature = "std"), feature(alloc))]
 
 #![cfg_attr(feature = "std", doc = "Substrate runtime standard library as compiled when linked with Rust's standard library.")]
 #![cfg_attr(not(feature = "std"), doc = "Substrate's runtime standard library as compiled without Rust's standard library.")]

substrate/core/sr-sandbox/src/lib.rs

@@ -37,7 +37,6 @@
 #![warn(missing_docs)]
 #![cfg_attr(not(feature = "std"), no_std)]
 #![cfg_attr(not(feature = "std"), feature(core_intrinsics))]
-#![cfg_attr(not(feature = "std"), feature(alloc))]
 
 use rstd::prelude::*;
 

substrate/core/sr-std/src/lib.rs

@@ -19,7 +19,6 @@
 
 #![cfg_attr(not(feature = "std"), no_std)]
 #![cfg_attr(not(feature = "std"), feature(core_intrinsics))]
-#![cfg_attr(not(feature = "std"), feature(alloc))]
 
 #![cfg_attr(feature = "std", doc = "Substrate runtime standard library as compiled when linked with Rust's standard library.")]
 #![cfg_attr(not(feature = "std"), doc = "Substrate's runtime standard library as compiled without Rust's standard library.")]

substrate/core/trie/src/lib.rs

@@ -17,7 +17,6 @@
 //! Utility functions to interact with Substrate's Base-16 Modified Merkle Patricia tree ("trie").
 
 #![cfg_attr(not(feature = "std"), no_std)]
-#![cfg_attr(not(feature = "std"), feature(alloc))]
 
 mod error;
 mod node_header;