Implement helper functions balanced_wait_until and balanced_awaken
They include new path for Windows 8.1+ (WaitOnAddress)
shared_mutex, cond_variable, cond_one, cond_x16 modified to use it
Added helper function utils::popcnt16
Replace most semaphore<> with shared_mutex
Rewrite to use unsigned arithmetic, shrink to u32
Ensure zero default unlocked state (will need it later)
Inline all public methods, rewrite lock_upgrade()
Remove try_lock_degrade(), lock_degrade() methods
Implement lock_downgrade() (now trivial)
Remove is_reading(), added is_free()
Added reader_lock::try_upgrade()
