Change ValueObject initializer

[pjaspers]

So while testing support for multiple rubies: see #63 (which is also included in this one) we ran into some deprecations in ruby 2.7, these had the following characteritic:

class Hi
  def initialize(hash)
    puts hash
  end
  def self.with(hash)
    new(hash)
  end
end
class HiAgain < Hi
  def initialize(it: "me")
  end
end
hi = Hi.with(it: "me")
HiAgain.with(it: "stinkt")

The Hi.with is fine, that's just a hash, but when we use the HiAgain class with a keyword initializer, ruby will complain that we're using the last arguments as keyword arguments and that will break in ruby 3. (We're passing keyword args to a hash param)

The obvious solution would be to ** double splat, but that comes at quite a performance cost.

So this takes a different approach, by copying/stealing some code from Sequel to have our ValueObject be configured with the fields once, and then setting the values to one hash in instance variable.

The good news is that it does shave off some allocations, the bad news is that I don't see any real performance benefit. So keeping this in draft for now.

[pjaspers]

@mestachs I'd be curious to know if this is performing better on Linux than on Mac

The other thing is, I think I might have made loading from yaml slower, so that will be annoying as well to compare (since both this spec suite, and the 'data-tests' in orbf2 use it as well)

But for what it's worth on travis it seems to behaving similarly to master (7.74s vs 7.75s)

[pjaspers]

@pjaspers rebase this against latest