doc, document output behaviour tweaks

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
minor, don't demand a space after `!'

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
minor, provide supp-diff operator (@)

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
test, provide regression tests for suppress-diff (@) feature

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
Merge branch 'feat/suppdiff'

* feat/suppdiff:
  test, provide regression tests for suppress-diff (@) feature
  minor, provide supp-diff operator (@)
  minor, don't demand a space after `!'
  doc, document output behaviour tweaks