Move TMXLayer.initArray call to initFromJSON method

- This small change will make using the TMXLayer API easier.
fixed collision check for objects outside of the viewport

this is still however configurable through the `alwaysUpdate` flag as
before, as the container object main loop will call the update function
or not based on the `inViewport` and `alwaysUpdate` flag
these are not required anymore :P
Update comments (no code change)
pass [dt] to the body update function

this does not change anything for now, as the body update does not do
anything with it yet, but this is for consistency, and to get people
used to do it (for futur usage)
fixed a small typo in the documentation
readme update
Revert "fixed a small typo in the documentation"

This reverts commit 14d1fae79d1fd447d2ef2610a0dcbe6b8f53c835.