Create godoc-friendly examples

[aol-nnov]

Move tests from the diskfs.go global comment section and update them as they are slightly out of date.

@deitch while trying to put my examples together I've found out that code snippets from the header comment block are slightly out of date.

I've converted them to the godoc-friendly versions and also left one FIXME item, as I'm not sure how it was intended to work here. Please advise how to fill gpt structures to match the comment above that example.

[aol-nnov]

Also, i'd like to make lint checks more loose in examples, but as failing CI shows, totally disabling them is a bad idea..

[deitch]

Looks like vet fails the examples. But I like this setup.

[aol-nnov]

I'm out for today... Will try something in near future - tomorrow or may be on Wednesday...

If you have any ideas how to make linter have softer checks for examples, please let me know...

[aol-nnov]

@deitch if you like those check() and unused(), there is one more action item left and then it's ready for merge.

[deitch]

Yeah, it's nice.

[aol-nnov]

Okay, and what about that last action item?

Should Start be 1*1024*1024/512 and Size be 10*1024*1024?

To be frank, for me, generally, it's a bit counter-intuitive, that Start is in sectors and Size is in bytes....

[deitch]

Okay, and what about that last action item?

Oh, I missed that. Sure, those numbers are as good as anything else.

[aol-nnov]

Done.

I just wanted to make sure, those numbers match the description comment above the example.

[deitch]

Thanks! Good to have you contributing here.

[aol-nnov]

Yay, updated docs have finally landed! https://pkg.go.dev/github.com/diskfs/go-diskfs@master

Pretty! 🎉