Atlas builder - support for repeat and loop dir properties of animation tags

[MarcinKuder]

Added generation of 'repeat' count and 'loop_direction' to fully support Aseprite's tag properties. This can be useful for example to play some animations once (e.g. death animation).

This will now generate the following code:

.. and it can be used in animation_update like this:

I've also extracted generated package name and input texture folder into constants for easier change.

[karl-zylinski]

Thanks a bunch! Great feature