Rewrite semaphore initialization, add end semaphore

Rewrite semaphore initialization, add end semaphore

It is better to create semaphores at 0 than at some value and then
subtracting them to 0.

The end semaphore will be used to signal to philosophers they should
end. This mechanism was chosen instead of kill function, because the
philosophers have to clean after themselves and signal
handlers cannot be used.