Add centralized config file

[tollmanz]

Based on a recommendation from @bradyvercher, there should be an easier way to share configs for Ostrichcize across WordPress installations.

[bradyvercher]

Sorry for not opening this beforehand myself, but the idea just came to me. I haven't thought through the specifics much, but maybe an environment variable might be the best place to define where the config is located. And while it might not be the ideal format, JSON is probably the most portable and will keep the plugin slim.

The other part is making the pattern matching a bit more generic rather than only allowing paths.

Thanks for considering this!