[#4] limiting: Add limiter

Signed-off-by: Aleksey Savchuk <a.savchuk@yadro.com>

limiting/semaphore/semaphore.go

@@ -0,0 +1,27 @@
+package semaphore
+
+import (
+	"sync/atomic"
+)
+
+type Semaphore struct {
+	count atomic.Int64
+	limit int64
+}
+
+func NewSemaphore(size int64) *Semaphore {
+	return &Semaphore{limit: size}
+}
+
+func (s *Semaphore) Acquire() bool {
+	v := s.count.Add(1)
+	if v > s.limit {
+		s.count.Add(-1)
+		return false
+	}
+	return true
+}
+
+func (s *Semaphore) Release() {
+	s.count.Add(-1)
+}