fix: rspec matcher [#60]
add Wisper#subscribe method [#66]

which replaces both .with_listeners and .add_listener
Merge pull request #72 from artmees/master

alias global and temporary listener methods to "subscribe" for consistancy
Merge pull request #71 from krisleech/rspec-matcher

fix: rspec matcher [60]
Allow invocation of event to be changeable [wip] [#38]
tidy up spec for send invoker [#38]
Add a logger invoker
use `anything` instead of `nil` in spec where value does not matter