Add the ability to specify a frame range

[cupojoe]

It would be great to be able to specify a starting and/or ending frame

> puppeteer-lottie -i input.json -o out.gif -s 5 -e 100
> puppeteer-lottie -i input.json -o out.gif -s 5
> puppeteer-lottie -i input.json -o out.gif -e 100

Ideally, it would be smart enough to use the last frame if the -e frame is larger.

[msqar]

Yes, it sucks that my animation is suuuuper slow :( it was set to have 180 frames, when the actual animation has like 70 frames.