ink! abi followup (#168)

* [examples] remove unneeded dependencies

* [cli] template: remove unneeded dependencies

* [*] make test-env a default feature

* [core] no longer export impl_empty_flush_for macro

* [scripts] add usage docs to check-workspace

* [readme] add section about scripts

* [core] add lib.rs docs

* [core] simple Cargo.toml formatting

* [ci] use latest nightly-2019-08-13

* [ci] upload kcov results after workspace checks

* [scripts] fix the banner not being printed

* Update README.md

Co-Authored-By: Andrew Jones <[email protected]>

* Update core/src/lib.rs

Co-Authored-By: Andrew Jones <[email protected]>