Add CURL advisories data source

[pombredanne]

See https://curl.haxx.se/docs/vulnerabilities.html and https://curl.se/docs/security.html
The actual sources are in https://github.com/curl/curl-www/tree/master/docs
And there are perl scripts to generate the tables.
DO NOT scrape the web pages. Use the repo and scripts instead.

[pombredanne]

The data is also in JSON at https://curl.se/docs/vuln.json
Some come also with patches like in https://github.com/curl/curl-www/blob/master/docs/CVE-2023-38545_patches.zip The horse's mouth is always going to be a better data than alternative sources.

[ambuj-1211]

Hey! @pombredanne I found this issue quite interesting. Looking forward to make great contributions to vulnerablecode including this one.
Do I need to make a separate branch for this in my fork?