Support PHP 8.0 and 8.1 syntax (without Attributes)

Added

• Support new PHP 8.0 and 8.1 syntax hilighting and indentation
  • [8.0] match expression (#632)
  • [8.0] mixed pseudo type declaration (#633)
  • [8.1] enum statement (#653)

Changed

• Drop support for Emacs 24 and 25.1 (#654)
• Raises an error when the byte-compiled Cc Mode version does not match that version at runtime.
  • You will need to recompile php-mode after the GNU Emacs version changes.

Removed

• Remove (require 'add-log)

Fixed

• Fix font-lock highlighting
  • != (#630)
• Fix Heredoc and Nowdoc highlighting (#651 thanks @antoineB!)
• Fix documentation mistake
  • php-mode-lineup-cascaded-calls in README.md (#644 thanks @cweiske!)