Make nullability explicit (not only) in ArrayType and CompositeType

README.md

src/Column.php

src/Conditions/IsEqualTo.php

src/Conditions/IsGreaterThan.php

src/Conditions/IsGreaterThanOrEqualTo.php

src/Conditions/IsIn.php

src/Conditions/IsLesserThan.php

src/Conditions/IsLesserThanOrEqualTo.php

src/Conditions/IsNotEqualTo.php

src/Conditions/IsNotIn.php

src/TableManager.php

src/Types/ArrayType.php

src/Types/CompositeType.php

src/Types/NullableType.php

src/Types/functions.php

tests/Types/ArrayTypeTest.phpt

tests/Types/CompositeTypeTest.phpt