v0.4.0

• enumerations can now leverage Psalm templates #24,
• enums sourced from PHP 8.0 #[Attribute]s in AttributeEnumTrait and AbstractAttributeEnum #28,
• getInstances() method to get instances of all members of given enum #30,
• isMemberWarm() method to check whether instance for given member was already requested #31,
• collection methods #30:
  • membersExist() to check whether all given members exist,
  • valuesExist() to check whether all given values exist,
  • isIn() to check against list of instances,
  • hasMemberIn() to check whether member is contained within given list,
  • hasValueIn() to check whether value is contained within given list,
• CI updated to use all PHP versions up to 8.3,
• Dropped Travis,
• Upgraded dependencies,