Use libcurl instead of curl

[concatime]

This is a proposition to replace calling curl by using libcurl directly. Hermes already uses libsignify instead of signify, internal sha256 implementation instead of sha256sum and libarchive instead of tar. So why not libcurl? This way, all dependencies are fetched at compile-time and not run-time. WDYT?

[andrewchambers]

I think its a good idea, though I did some work on the second generation of hermes which works a bit differently so I'm still deciding what the best course of action will be.