Add support for file request paging to Remote::FindParentById

[arolett2]

While issuing pull requests on a few of my directories I noticed that
I was missing files. Implement paging so pull requests on directories
that have more than 100 files work.

[rakyll]

We should have a better and interactive pagination strategy. We shouldn't stall if a directory contains too many children.

[arolett2]

Thanks for taking a look!
So I understand are you suggesting a change to the user workflow (pull only operates on a set number of files unless you tell it otherwise ... and just warns you if there are too many files) or are you just talking about the internal API?

For the internal API flow are you imagining FindParentByIdFirst/Next/Close flow for the API?

For a pull request it seems like we need to know all of the files for changes.go so we can figure out what to sync down. But I see how we could improve things by processing the changes in batches. I'll take a look a bit later.

[rakyll]

Sorry for catching up so lately.

The more pleasant behavior is to have interactive cursoring, so the user can cancel on any time. But it will require some more work, will break some upcoming features as well. So, let's merge this PR first and I'll make improvements on the top this change.

[rakyll]

There is a flag now that allows you not to ignore the hidden files. Could you honor that?

[arolett2]

Changed.