Add CURL detection

[Francisco Presencia]

I'd like to suggest adding CURL support. Curl shows up as:

curl/7.64.1

So I'd like to suggest adding CURL parsing resulting in:

{
  name: "curl",
  version: "7.64.1",
  os: null,
  type: "bot"
}

Is this okay? I can make a PR according to the docs, but was unsure about both the "os" and "type" field.

[Damon Oehlman]

@franciscop I'm definitely in favour of this. I think null is good for the os for now. At some point I might look at converting the null return result to an additional literal of unknown but that would be for later and a major release as it would be a breaking change. So I think what you have suggested in this issue, is perfect 👍🏻

[Francisco Presencia]

Done! Not exactly as I originally suggested, since it seems the code "guided me" to a slightly different structure, see the PR for details.