1.4

enable forking of Modes and add ImmutableMode

 - make sure the default empty Mode is immutable

1.3

add CombinedInvoker and utility methods and constants

• add default constants for Mode and Invoker
• add overrides for invoke methods without mode that use the default
  Mode constant

1.2.2

upgrade gradle wrapper

1.2.1

remove bintray plugin, update dependencies and increment version

1.2

refactor ReferenceCountedMutex

 - remove synchronisation when removing mutex from map since the mutex
   is only removed once when decrementing the rc to 0
   - this is now guaranteed since the rc cannot increment once reaching
     0 anymore