* Test against `roave/you-are-using-it-wrong`
* Added CI step to ensure BC of declared API
* Added step to ensure `composer.json` has all used deps
* Including CI check tools as dev dependencies
* Typo fix: s/backwards/backward
* Run `roave/backward-compatibility-check` off an isolated location with no other dependencies
* Run `test-with-real-projects` task with PHP 7.4 as base runtime
* Run `testing-with-real-projects` also against `ocramius/proxy-manager`
`ocramius/proxy-manager` is an extremely heavy `vimeo/psalm` consumer,
and relies on a lot of the templated types system to generate real
types for proxies produced by runtime evaluation.
