Phillip/spur integration

[phillip-stephens]

Adds support for the Spur IP intelligence data feed. Pasting README content here for description:

Spur IP Enrichment + Intelligence

spur.us provides per‑IP intelligence such as ASN and organization, infrastructure classification (e.g., datacenter, CDN, mobile), and geolocation metadata.
We can query spur.us alongside other sources to enrich annotations and help identify datacenter/Anycast deployments, CDNs, and ISP ownership.

0. You'll need an API key from Spur to enable ZAnnotate to enrich IPs with their dataset as we'll need to make an API request for each IP address to be enriched.
   Depending on current pricing, you may need to sign up for a paid account.
   Check out spur.us/pricing for more details.
1. Once you have an API key, set it as an environment variable in your current shell session:

export SPUR_API_KEY=your_api_key_here

(If you want to make this permanent, add the above line to your shell profile, e.g. ~/.bashrc or ~/.zshrc)
2. Test with:

$ echo "1.1.1.1" | ./zannotate --spur

Example Output:

{"ip":"1.1.1.1","spur":{"as":{"number":13335,"organization":"Cloudflare, Inc."},"infrastructure":"DATACENTER","ip":"1.1.1.1","location":{"city":"Anycast","country":"ZZ","state":"Anycast"},"organization":"Taguchi Digital Marketing System"}}

Associated Issues

Closes #54