Adds counting semaphores

An attempt on implementation of counting semaphores requested in Issue #162 , both mutex and java implementations should be working

Two questions about ```reduce_permits```:
first, in Java it is a protected method used (according to the docs[1])  ``` in subclasses that use semaphores to track resources that become unavailable```. Is this method needed?

second, does it make sense to raise an error if doing the reduce would bring available permits below zero? Another approach would be to reduce available permits to zero if anyone attempted to do this

[1] https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/Semaphore.html#reducePermits(int)
I did some more testing, see https://gist.github.com/pitr-ch/43fd7c52f01e0cc56cea The tap is slower in the end but only a little. Big surprise for me, thanks @adamruzicka for bringing it up.