Basic support for name mode queries

[ghormoon]

Initial support for queries having name= arguments instead of pre-crafted dns= argument.
type= is optional, default is 'A' if not provided.

I'd appreciate any feedback and more testing in different usecases (e.g. I'm not sure how to properly test the scrub condition, I didn't make it work with dns= either in my usecase)

this feature is extremely useful if you want to use if tom some app (including from another njs function as subrequest) that doesn't know how to craft the dns query and you don't want to re-implement it.

example usage

var reply = await r.subrequest('/dns-query?name=' + hostname + '&type=A');

fixes #30 and #25 (and potentially others that i missed or didn't explicitly state what query are they using, but have simmilar backend errors)