Not compatible with multi-sites

[watarutmnh]

Currently it only share primary site's entry url.
I wish if the plugin compatible with multi-sites.

[reganlawton]

I'm open to a PR but due to my time and the simple features of the plugin, I can't at this time assign the time to looking into the multi site side of the plugin.

[RickKukiela]

Since I already have a fork for my last PR I might look into adding it but its gonna be low on my priority list.

[RickKukiela]

I just realized I never looked at this and forgot all about it! I'll put it on my rainy day todo list and see what can be done. It shouldn't be very hard to add!