Disable comment should apply to the next line of source code

[backus]

I intentionally didn't implement this before because I just wanted to get something simple out first to begin playing with it, but I've already run into a case where I was surprised because I had something like

# Method docs
#
# mutest:disable
# rubocop:disable Metrics/MethodLength
def foo
  blah
end

and the disable comment didn't apply because it currently just filters out the literal next line.

Opening this issue as a reminder of an easy and obvious improvement to add soon

[backus]

Realistically, until these support something like # mutest:disable NegateReceiver they should just be rewritten to use the same code path as ignore_subjects