* srml-contract: Move gas costs from Config to Schedule.

* srml-contract: Define Gas units fixed as u64.

This removes Gas as a configurable type on the contracts Trait.

* Bump node runtime spec/impl versions.

* Pass input data via the scratch buffer.

Remove calls to ext_input_*.

* Fix tests and docs

* Bump the version.

* Remove ext_input_* from COMPLEXITY.md

* Return back the length check and add more comments

* Update the documentation of the scratch buffer.

* Fix a silly mistake.

* srml-contract → srml-contracts

* Trim.

* Bump version