This ensures the deno executable is properly created before running the integration tests.
Also allows deno_cli to be used as a lib. Docs are now properly generated: https://docs.rs/deno_cli/0.18.4/deno_cli/
Towards #2933
Prep for #2955
A major API change was that asserts are imported from testing/asserts.ts
now rather than testing/mod.ts and assertEqual as renamed to
assertEquals to conform to what is most common in JavaScript.
