fix for #36: account for nested `.publish()` invocations and dequeue all queued `.unsubscribe()` calls which occurred during that time.
Merge branch 'issue-36' of https://github.com/GerHobbelt/postal.js into GerHobbelt-issue-36
Merged and tweaked PR from @GerHobbelt, which fixed issue with nested publishes breaking the unsubscribe queue behavior
Bumped version and updated contributor list to add @GerHobbelt