Start/stop HTTP servers when enabling/disabling REST module

Update CI to use actions/checkout@v3

Add early-out to ecs_set when there are no observers or hooks registered

Remove redundant assignment in sparse set code

Transfer ownership of world to app after app().run()

Add README on how to run examples

SanderMertens#778 regression issue where components in C++ weren't cr…

…eated with low ids

Fix typo in example

Added const variants for flecs::ref methods

SanderMertens#124 add more observer tests, fix issues