Investigate helper functions

[AngelMunoz]

taken from #1
add method helpers to create things like filters, fields, matching criteria

examples of this can be

find "users" {
  filter (fun m -> m.prop = value)
}

or

find "users" {
  filter "prop" gt 10
}

the main blocker right now for this is that in any case, we must emit 100% compatible JSON to https://docs.mongodb.com/manual/reference/command/
so there needs to be some investigation around this if this is something people want to add into the mix

[AngelMunoz]

@Alkasai: I like the new typed results!
What do you think about wrapping this into some sort of function that just returns seq of type User, instead of cursor?

let result = db.RunCommand<FindResult<User>>(JsonCommand over20)
printfn $"FindResult Ok: %f{result.ok}"
result.cursor.firstBatch |> Seq.iter (fun value -> printfn $"%A{value}")

This seems like a useful addition, we should make a list of functions that can help