Implement delay between saved pages in batch save urls

[kuolemaaa]

Something like

1. load i-th website
2. save i-th website
3. wait a bit
4. next i: goto 1

this in order to avoid to trigger sorts of rate limiter

[logistic-bot]

I would also really like this feature.

To clarify: We would like a way to configure a delay between the saving of each page in a batch, to prevent hitting server-side limits.
An additional option so that the delay is only between different domains would be really nice, but not essential.

[gildas-lormeau]

I've implemented the hidden option delayAfterProcessing (see https://github.com/gildas-lormeau/SingleFile/wiki/Hidden-options). It will be available in the next version.