Add digest subtypes and update dependencies (#2734)

* Add different digest types for different parts of the code

* Add script to update dependencies

* Remove an old changelog

* `Inherent` → `PreRuntime`

substrate/core/sr-primitives/src/generic/mod.rs

@@ -36,7 +36,9 @@ pub use self::era::{Era, Phase};
 pub use self::checked_extrinsic::CheckedExtrinsic;
 pub use self::header::Header;
 pub use self::block::{Block, SignedBlock, BlockId};
-pub use self::digest::{Digest, DigestItem, DigestItemRef};
+pub use self::digest::{
+	Digest, DigestItem, DigestItemRef, ConsensusDigest, RuntimeDigest, SystemDigest,
+};
 
 use crate::codec::Encode;
 use rstd::prelude::*;