The parser will now always generate Identifier nodes (for
non-namespaced identifiers). This obsoletes the useIdentifierNodes
parser option.
Node constructors still accepts strings and will implicitly create
an Identifier wrapper. Identifier implement __toString(), so that
outside of strict-mode many things continue to work without changes.
Magic constant names have been added after the PHP 7 release.
We do not support and likely will not support __halt_compiler here
due to lexer limitations.