Flush world before reaction iteration

[keis]

This fixes the issue I was facing reported in #22

I'm not sure it's a good solution but it's A solution. Apply the deferred commands after each iteration likely has some real cost :shrug:

[viridia]

BTW, if you wanted to reduce the performance hit, you could call flush at the beginning of the loop, but only after the first time. So it would only happen between reactions.