Add option for a delay between request about percollate

[danburzo]

Hi @XiangRongLin, thank you for the report. In general, I've avoided implementing options for fetching pages, since that opens up a whole new dimension of configuration (do we support delays / parallelism? proxies? authentication headers? etc.). Instead you are able to use a combination of - and --url to offload the responsibility to a separate program (eg. curl) as below:

curl https://example.com | percollate pdf - --url=https://example.com

For bundling multiple pages into a single EPUB, the workaround is admittedly a bit convoluted:

1. fetch each page using curl and feed it to percollate html with the - operand and the --url option, using your desired parallelism and delay between requests.
2. feed all local HTML pages to percollate epub.

It might make sense to introduce an option to control parallelism and delay, such as:

percollate epub --wait=N url1 url2 ...

When --wait is supplied, percollate could switch from fetching in parallel to fetching sequentially, with a delay of N seconds between requests.

[danburzo]

The --wait option has been published in [email protected].