0.5.0 release

This is maintenance release that’s been showcased in a game Cycle of Evil, check it out!

This release includes the following important changes:

• keyword argument :MISSING-ERROR-P to unique indices allowing not to throw an error when entity is not found;
• error messages for entity being not found in indices made clearer by mentioning component name;
• ability to define and use components in different CL packages;
• ability to delete previously registered system;
• SYSTEM-EXISTS-P helper to check whether system exists by its name;
• style warnings when component slot types would be boxed by CL implementation, hence incurring performance penalty;
• a hook for entity deletion;
• fixed subtle bug when entity with deleted component would be incorrectly processed by system when it shouldn’t;
• the component data is now not lost upon component redefinition ✨

See changelog for a full list of changes.