rename module which is included from Wisper to Wisper::Publisher
Raise when Wisper is included (old syntax) instead of Wisper::Publisher (new syntax)
Rename wisper_spec to wisper/publisher_spec
#listeners returns a collection of listeners, not registrations.
add spec for .add_listener alias
Raise more descriptive exception message [ci skip]
Instead of raising an exception when old syntax used handle it maintaining backwards compatibility, meaning we do not have to go to v2.0 yet.
Merge branch 'v2.0'
Despite the branch name, this isn't v2.0 since it has been made to be backwards compatible.