Code quality updates

Minor code quality updates

3.0.0

Merge pull request #27 from mindplay-dk/3.0.0

3.0.0

Maintenance release

Fixes a deprecation notice under PHP 7.4.

Bugfix release

With this release, Container will throw a ContainerException if a circular dependency is encountered.

The previous version allowed certain kinds of circular bootstrapping, but (due to an implementation detail) under certain circumstances would satisfy a circular dependency by generating two instances of the same component.

Tweak

Clarifies an exception message.

Maintenance release

This release improves forward compatibility with the final PSR-11 package.