[fixedmap] make fixedmap a LRU cache

Signed-off-by: eater <=@eater.me>

fixedmap.go

@@ -38,6 +38,8 @@ func NewFixedMap(size int) *FixedMap {
 func (fm *FixedMap) Get(key string) *File {
     elem, ok := fm.Map[key]
     if ok {
+        /* And that's an LRU implementation folks! */
+        fm.List.MoveToFront(elem.Element)
         return elem.Value
     } else {
         return nil