SDLx::Sprite::Animated need random start frame

[kthakore]

When I set many units on map they all move equally (in lockstep).
Now just one possible code to do that:

after constructor

$anim->next for 0 .. rand 10;

but this is very ugly =(

I think we need add param in constructor: randomize => 1, and/or param/function to set start frame manually.

[jtpalmer]

I'd like the ability to change the frame manually (not just in the constructor). SDLx::Sprite::Animated::current_frame() returns the frame number, but I'd like to use that method to change the current frame as well.