disable coverage generation (it's unstable)
Syncable optimizations:
 - SomeSyncable.defaults contains defaults for all the fields (from parent type too);
 - reset() don't iterate over type hierarchy any more;
 - reset() invoked in Syncable once;
 - once() allow passing object with "deliver" as a callback.
Set fixes:
- "init" reaction (correct this value);
 - prevent double proxy-subscriptions when the same entry added to set twice.