Add pluralS function for prettyprinting
BounceParameter type (used to be Either)
Code style refactoring
Introduce worker watcher, refactoring

The worker watcher watches workers on a ThreadId level, and kills them
when they haven't entered the database after a certain amount of time.
Housekeeping module
yellAndRethrow: add modifier function
Add restarter function (but don't use it yet until leak is fixed)
Doc only
Add difficulties meta-information file