Resume support

[nateraw]

Continuation of #35 by @codefaux. Separated to new branch so I could safely fix history issues without damaging original PR.

I moved resume to be a kwarg instead of separate function. Here's how I'm using it:

Given an unfinished run at dreams/20220912-100023, I run this:

walk(
    output_dir='dreams',
    name='20220912-100023',
    resume=True
)

[nateraw]

Thanks again for your work here @codefaux !! lmk if I missed anything. Merging for now.

[codefaux]

Hey thanks, glad to see it used. It's been a very useful feature, and the only reason I'm willing to tackle things like my 10,000 frame "daydream" videos project. I'm excited to see what else it enables others to consider creating. Looks like it should even resume my current run without issue, which is always a bonus. Good working with you.

[nateraw]

If any other feature requests come up, feel free to drop them in the issues section 😄 . Was great workin with you on this.