Collect Murmur Hash of Favicon

[0xdade]

Is your feature request related to a problem?
The Nmap http-favicon script is pretty unreliable and doesn't produce a result that is easily searchable. Instead it produces a text output based on whether or not that favicon is known in the nse.

Describe the feature you'd like
Build support for the agent to fetch favicons for each http service and store their mmh3 value.

Have you considered alternative ways to get this feature
If I were writing this capability (which I probably will be), I'd do it something like this:

1. Getting the favicon from <link> tag:
   1. If web_screenshot is enabled then get raw html data from web_screenshot
   2. If web_screenshot is not enabled, requests.get(target)
2. Look for link tags with rel="icon" attribute. If found:
   1. r = requests.get(href_from_link)
3. If no link tag, try to fetch default favicon
   1. r = requests.get(f"{target}/favicon.ico")
4. If r.status_code == 200:
   1. favicon = codecs.encode(r.content, "base64")
   2. hash = mmh3.hash(favicon)

Additional context
This will provide the ability to look for hashes that you might already see in public services such as shodan, and favicons are small enough that a cryptographic hash such as md5 or sha256 would be overkill.