TODO-5.1

Zend Engine
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  - Look at making zend_constant value member be a zval* instead of zval. (Andi)
  - Implement inheritance rules for type hints. (Marcus) 
  - Implement typehinting for arrays (apply the patch). (Andi, Marcus)
  - Find a keyword for the if-set-or operator (apply the patch). (Marcus, all)

Standard Library
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  - Implement new time/date parsing and handling functions. (Derick)