Add basic BABE consensus type (#2165)

* Add basic BABE consensus type

* Update core/consensus/babe/slots/Cargo.toml

Co-Authored-By: DemiMarie-parity <48690212+DemiMarie-parity@users.noreply.github.com>

* Fix parameterization and run `rustfmt`

* Respond to review comments

* Update various Cargo.lock files

* Revert "Update various Cargo.lock files"

This reverts commit af53d7624752a744320e9cbb25749fdd8e6f46d2.

* `BabeSealSignature` → `BabeSeal`

* Move slot code to its own crate

This was highly non-trivial, due to cyclic dependencies.

* Remove redundancy between AuRa and BABE

Some of the code duplication was removed using a macro.

* Fix build error

* Avoid non-`#[doc(hidden)]` re-exports

Also, bump some library versions in `Cargo.toml`.

* Remove dead code in AuRa

* Remove impl_slot macro

It was more trouble than it was worth.

Also, delete useless dependencies on Serde.

* AuRa and BABE need different DB keys

* Bring back `aura::Network`, but deprecate it.

* Improve docs and add `slot_duration` inherent method

* Add docs to `substrate_consensus_aura::SlotDuration`

* Add missing documentation and #![forbid(missing_docs, unsafe_code)]

* Add a #![forbid(missing_docs)]

* Remove dependency of `test-runtime` on `slots`

* Update core/consensus/babe/src/lib.rs

Co-Authored-By: DemiMarie-parity <48690212+DemiMarie-parity@users.noreply.github.com>

* Remove wrongly added file

* Fix copyright notice

Co-Authored-By: DemiMarie-parity <48690212+DemiMarie-parity@users.noreply.github.com>

* Bump `impl_version` and `spec_version`

* Fix deprecation version; remove spurious carets

* Update Cargo.lock

* Update dependencies

substrate/core/sr-api-macros/Cargo.toml

@@ -8,8 +8,8 @@ edition = "2018"
 proc-macro = true
 
 [dependencies]
-quote = "0.6"
-syn = { version = "^0.15.22", features = [ "full", "fold", "extra-traits", "visit" ] }
+quote = "0.6.12"
+syn = { version = "^0.15.30", features = [ "full", "fold", "extra-traits", "visit" ] }
 proc-macro2 = "0.4"
 blake2-rfc = "0.2"
 proc-macro-crate = "0.1.3"