I've added a plugin using the same architecture as the prowlarr plugin
to enable Newznab as a source.
I've tested locally with nzbhydra2 and it all seems to work as intended.
I've added some unit tests for this feature, and found that a couple of
other unit tests weren't behaving so fixed those up while I was at it. I
also ran all of the linters in the makefile against it and fixed those
up, too, so hopefully this should be as clean and as compatible as it
can be.
