3.0.1: Children iteration fix

• Fixed xp-framework/compiler#71: Call to a member function children()
  on array, which occured with if, catch and switch statements
  as well as for array literals.
  (@thekid)

3.0.0: Element -> Node, Code generator

• Heads up: Changed transformation API - functions must accept a
  reference to the code generation process as their first parameter.
  (@thekid)
• Heads up: Added kind to UnaryExpression constructor which is
  either prefix or suffix, supporting ++$i as well as $i++.
  (@thekid)
• Merged PR #4: Add Node class replacing Element and Value - @thekid

2.0.0: Compact AST

• Merged PR #3: Allow multiple transformations per kind - @thekid
• Heads up: Removed Symbol and Node classes, which belong to the
  compiler internals now only
  (@thekid)
• Merged PR #2: Refactor AST. This makes programmatic AST creation far
  easier and improves on memory usage.
  (@thekid)

1.4.0: PHP 7.4 compatibility

• Made compatible with PHP 7.4 - refrain using {} for string offsets
  (@thekid)

1.3.0: Using

• Added lang.ast.nodes.UsingStatement in preparation for adding support
  for the using statement in xp-framework/compiler#33
  (@thekid)

1.2.0: Constant types

• Added type to class constants - @thekid

1.1.0: Mixed type

• Added support for mixed type - @thekid

1.0.1: Nullable fix

• Fixed nullable value types being emitted incorrectly - @thekid

1.0.0: Extracted from XP Compiler

• Extracted from XP Compiler, see xp-framework/compiler#22 - @thekid