feature/enhancement

[hamhoney]

Hi @maddyb99 !
Your shimmer_animation package is very helpful.

I tried to using shimmer_animation and found that I need two features.

• The ability to animate in one-shot mode.
• A delayed start(as mentioned in issue Synchronize a group of shimmer animations #17 )

I have also added example code, so you can see the changes!

Please check my pull request codes.
Thanks!