Add multisite support

[theMikeD]

Add support for --url option, for proper use in multisite environments

[8ctopus]

@theMikeD Awesome work!
@trepmal Do you plan on reviewing the PR? If not, README should state than multisite support is not planned.

[8ctopus]

@theMikeD Maybe you could enable issues in your repository while waiting for the PR approval? This way other users can install your flavor of the package.

[trepmal]

Thanks for the ping @8ctopus , my personal email inbox is a bit untamed at the moment.

Multisite support should be there out of the box. A quick test correctly gave be different results for wp revisions list. Is there a specific situation where you're seeing incorrect behavior or getting an error?

trepmal production ~ $ wp revisions list --url=<redacted>
+----+------------------+-------------+
| ID | post_title       | post_parent |
+----+------------------+-------------+
| 46 | Roman-Middle     | 9           |
| 45 | Roman-Middle     | 9           |
| 44 | Roman-Middle     | 9           |
| 43 | Roman-Middle     | 9           |
| 42 | Roman-Middle     | 9           |
...
+----+------------------+-------------+

trepmal production ~ $ wp revisions list
Warning: --url was not specified
List all 4654 revisions? [y/n] 

[8ctopus]

@trepmal Thank you for the quick reply, I did not test it as from the issue and from the PR multi-site doesn't work. Now that you answered, I will test and report back.

[8ctopus]

@trepmal I have tested it today and can confirm that the list command shows different revisions when I update the url

wp revisions list --url=https://.../blog/

Update: I tested all commands locally on my multi-site development installation and can happily confirm that the vanilla version works without the need for this PR, but maybe @theMikeD found cases where it doesn't work since he submitted the PR.