Request for the ability to build multiple pages in a single build with `--pages`

[pneedle-rh]

If my understanding is correct, it is only possible at present to build one page when using the --page or -p option. To build only the pages changed by a docs PR, my understanding is that we need to run asciibinder build --page=<page> multiple times. This seems to take some time if there are many pages changed by a PR.

For performance reasons, it would be great if AsciiBinder were updated to allow you to specify multiple pages for one --page argument, using commas to separate them. For example:

$ asciibinder build --page=<page>,<page>,<page>

This way, AsciiBinder could be optimised to build selected multiple pages pages in one AsciiBinder build run.

This relates to a script that I wrote that could potentially help with Travis checking for AsciiDoc errors and warnings in docs PRs.