fix join subscription obj
added test to prevent stopping join part
prevent joins of a single listenable
update code comments
travis-prompted cleanup
add test for 0 join listenables too
Merge pull request #97 from krawaller/preventsinglelinkjoin

prevent joins of a single listenable
Merge pull request #96 from krawaller/joinsubobj

fix join subscription obj
Bumped version
Updated build artifacts
Bumped version again

Not sure if the version was properly pushed as I forgot to update the
build artifacts.
Updated changelog with v0.1.14 and v0.1.15 updates