(FACT-1144) Add memory resolver for OpenBSD

[jasperla]

Currently without swap facts while those are being sorted out.

[MikaelSmith]

Mind commenting with the output from the resolver?

[jasperla]

{
  system => {
    available => "1.47 GiB",
    available_bytes => 1578127360,
    capacity => "59.23%",
    total => "3.61 GiB",
    total_bytes => 3870953472,
    used => "2.14 GiB",
    used_bytes => 2292826112
  }
}

[peterhuene]

We generally prefer c++-style casts over c-style casts (for various reasons). result.mem_total = static_cast<uint64_t>(uvmexp.npages << uvmexp.pageshift); should do it. Same comment for the line below.

[peterhuene]

Other than above minor comments, this looks good 👍

[jasperla]

I've fixed up the casts and declaration.

[peterhuene]

Looks like this block is unintentionally indented more than needed.

[jasperla]

That's also fixed now.

[HAIL9000]

@peterhuene, could you take another look now that it's been updated?

[peterhuene]

@jasperla Thanks again for the contribution!