Allow dynamic linking

[NaimKabir]

I want to be able to specify that go/who/{NAME} unpacks into: https://github.com/{NAME}.

This allows for more flexible links that plug into my workflow.

Use cases:

• Engaging multiple search engines from the browser: e.g go/google/{QUERY} vs. go/duckduckgo/{QUERY}
• Sanely exploring sub-domains: e.g go/r/{SUBREDDIT} -> https://reddit.com/r/{SUBREDDIT}

[NaimKabir]

The google DeclarativeNetRequest paradigm makes this difficult because it expects to have explicit URL-redirect rules. We'd need some kind of just-in-time creation-and-destruction of rules to make this happen—or switch paradigms altogether.

[NaimKabir]

Making sure to reserve 1000 IDs of the allowed dynamic rules space to see if we can use those for this feature in this #15