Release 2.1

Features

• Expanding method signatures for set, singleton, and factory to allow passing in an alias or an array of aliases to assign.
• Updating method signature for alias to allow a string or an array of strings for aliases.

Updates

• New copyright year in license.
• Updating documentation (adding alias docs.)
• Fleshing out Docblocks in Container.
• Bumping dev dependencies.
• Removing unused dev dependencies.
• Updating Github Actions config to add composer audit and validate.