func (s *Subscription) RemoveEntity(id EID) {
	if _, found := s.entityMap[id]; found {
		s.dirty = true
		delete(s.entityMap, id)
	}
}
RemoveEntity removes an entity from the subscription entity map
package akara
import (
	"sort"
	"sync"
)
type entityMap map[EID]*empty
type empty struct{}  
func NewSubscription(cf *ComponentFilter) *Subscription {
	return &Subscription{
		Filter:    cf,
		entityMap: make(entityMap),
		entities:  make([]EID, 0),
		ignoredEntities: make(entityMap),
	}
}
type Subscription struct {
	Filter    *ComponentFilter
	entityMap        
	entities  []EID  
	dirty     bool
	ignoredEntities entityMap
	mutex     sync.Mutex
}
func (s *Subscription) AddEntity(id EID) {
	if _, found := s.entityMap[id]; !found {
		s.dirty = true
		s.entityMap[id] = &empty{}
	}
}