start from 4.20 for automatic builds

fixed 4.18

fixed 4.21 build

Update README.md

ported to 4.15

fixed autodetection for PyFbxFactory #488

Merge pull request #504 from heylenz/master

pyactor add  function "set_actor_hidden_in_game"

added set_brutal_finalize()

fixed 4.18

Update MemoryManagement.md