* Add VL_ASSERT_CAPABILITY; add assumeLocked and pretendUnlock to V3Mutex.
* Pass jobs as template-arguments and use std::packaged_task.
* Add and use V3ThreadPool::ScopedExclusiveAccess.
`stopRequested()` reads only atomic variables. It doesn't need a mutex
to do this.
This function is called in `waitIfStopRequested()`, which in turn
is called before execution of every job, and inside some jobs. With this
change the mutex inside `waitIfStopRequested` needs to be locked only in
very rare cases instead of every time.
Kamil Rakoczy
Wilson Snyder
Mariusz Glebocki