Add GIF and JPEG (JFIF) specs

[tidoust]

This adds the GIF and JPEG specifications to the list, as requested in #1089.

For GIF, the most canonical URL is the specification published under w3.org, consistent with Specref and Wikipedia.

The notion of group does not mean much for the GIF spec. Also, the link to the CompuServe website seems a bit wrong, but a URL is needed...

For JPEG, the usual reference is to the interchange format (JFIF). A PDF version of the 1992 spec exists under w3.org at: https://www.w3.org/Graphics/JPEG/jfif3.pdf

That is the spec that Specref returns for JPEG. That said, JPEG is published and maintained by ISO/IEC under the name iso10918-5: https://www.iso.org/standard/54989.html

That spec (and name) is used in the list instead of the PDF version because it provides a more official entry point. If we want to record the public version from 1992 somewhere, a new "JPEG" or "JPEG-1992" entry could perhaps be created.

This would add the following entries:

[
  {
    "url": "https://www.iso.org/standard/54989.html",
    "seriesComposition": "full",
    "shortname": "iso10918-5",
    "series": {
      "shortname": "iso10918-5",
      "currentSpecification": "iso10918-5",
      "title": "Information technology — Digital compression and coding of continuous-tone still images: JPEG File Interchange Format (JFIF) — Part 5:",
      "shortTitle": "JPEG"
    },
    "shortTitle": "JPEG",
    "organization": "ISO/IEC",
    "groups": [
      {
        "name": "ISO/IEC JTC 1/SC 29",
        "url": "https://www.iso.org/committee/45316.html"
      }
    ],
    "title": "Information technology — Digital compression and coding of continuous-tone still images: JPEG File Interchange Format (JFIF) — Part 5:",
    "source": "specref",
    "categories": [
      "browser"
    ],
    "standing": "good"
  },
  {
    "url": "https://www.w3.org/Graphics/GIF/spec-gif89a.txt",
    "seriesComposition": "full",
    "shortname": "GIF",
    "series": {
      "shortname": "GIF",
      "currentSpecification": "GIF",
      "title": "Graphics Interchange Format",
      "shortTitle": "GIF",
      "nightlyUrl": "https://www.w3.org/Graphics/GIF/spec-gif89a.txt"
    },
    "shortTitle": "GIF",
    "organization": "CompuServe Incorporated",
    "groups": [
      {
        "name": "CompuServe Incorporated",
        "url": "https://www.compuserve.com/"
      }
    ],
    "nightly": {
      "url": "https://www.w3.org/Graphics/GIF/spec-gif89a.txt",
      "status": "Editor's Draft",
      "filename": "spec-gif89a.txt",
      "alternateUrls": []
    },
    "title": "Graphics Interchange Format",
    "source": "specref",
    "categories": [
      "browser"
    ],
    "standing": "good"
  }
]