v0.5.5

Fixes

• Global functions now declare enum return types. A generated global helper
  (features.use_functions) for a function returning a C enum declared its return
  as int|<wrapper>, but the entity it delegates to returns the generated PHP enum —
  so calling it (e.g. \Pnlx\Func\Libsdl\SDL_HasEvent(), which returns SDL_bool)
  threw a TypeError. The global function now returns <Enum>|null, matching the
  entity method.