v1.6.0

This release bumps the minimum required PHP version to 7.1.3.

Following improvements were introduced:

• ArrayCollection#filter() now allows filtering by key, value or both.
• When using the ClosureExpressionVisitor over objects with a defined
  accessor and property, the accessor is prioritised.
• Updated testing tools and coding standards, autoloading, which also
  led to marginal performance improvements
• Introduced generic type docblock declarations from psalm,
  which should allow users to declare /** @var Collection<KeyType, ValueType> */
  in their code, and leverage the type propagation deriving from that.

Total issues resolved: 16

• 127: Use PSR-4 thanks to @Nyholm
• 129: Remove space in method declaration thanks to @bounoable
• 130: Update build to add PHPCS and PHPStan thanks to @lcobucci
• 131: ClosureExpressionVisitor > Don't duplicate the accessor when the field already starts with it thanks to @ruudk
• 139: Apply Doctrine CS 2.1 thanks to @Majkl578
• 142: CS 4.0, version composer.lock, merge stages thanks to @Majkl578
• 144: Update to PHPUnit 7 thanks to @carusogabriel
• 146: Update changelog for v1.4.0 and v1.5.0 thanks to @GromNaN
• 154: Update index.rst thanks to @chraiet
• 158: Extract Selectable method into own documentation section thanks to @SenseException
• 160: Update homepage thanks to @Majkl578
• 165: Allow ArrayCollection#filter() to filter by key, value or both thanks to @0x13A
• 167: Allow ArrayCollection#filter() to filter by key and also value thanks to @0x13A
• 175: CI: Test against PHP 7.4snapshot instead of nightly (8.0) thanks to @Majkl578
• 177: Generify collections using Psalm thanks to @nschoellhorn
• 178: Updated doctrine/coding-standard to 6.0 thanks to @patrickjahns