Fixing bugs found when implementing Bidirectional Iterator unit tests.

-Fixed: AbstractList/ImmutableList/ArraySet/ArrayMap skip/back implementation was causing crashes and didn't update the last returned value.
-Fixed: ArraySet/ArrayMap previous was not subtracting before returning value.
-Fixed: BidirectionalIterator back was calling the object variant instead of the TypeSpecific Variant.
-Fixed: TreeSets/Maps Iterator now fully supports backwards Iterating.
-Added: Specialized skip/back function to improve speed in ImmutableHashSet/LinkedHashSet/CustomLinkedHashSet

src/builder/resources/speiger/assets/collections/templates/sets/LinkedOpenCustomHashSet.template

@@ -717,6 +717,28 @@ public class LINKED_CUSTOM_HASH_SET KEY_GENERIC_TYPE extends CUSTOM_HASH_SET KEY
 			return previous != -1;
 		}
 		
+		@Override
+		public int skip(int amount) {
+			int result = 0;
+			while(next != -1 && result != amount) {
+				current = previous = next;
+				next = (int)(links[current]);
+				result++;
+			}
+			return result;
+		}
+		
+		@Override
+		public int back(int amount) {
+			int result = 0;
+			while(previous != -1 && result != amount) {
+				current = next = previous;
+				previous = (int)(links[current] >> 32);
+				result++;
+			}
+			return result;
+		}
+		
 		@Override
 		public int nextIndex() {
 			ensureIndexKnown();
@@ -775,9 +797,8 @@ public class LINKED_CUSTOM_HASH_SET KEY_GENERIC_TYPE extends CUSTOM_HASH_SET KEY
 		@Override
 		public KEY_TYPE PREVIOUS() {
 			if(!hasPrevious()) throw new NoSuchElementException();
-			current = previous;
+			current = next = previous;
 			previous = (int)(links[current] >> 32);
-			next = current;
 			if(index >= 0) index--;
 			return keys[current];
 		}
@@ -785,9 +806,8 @@ public class LINKED_CUSTOM_HASH_SET KEY_GENERIC_TYPE extends CUSTOM_HASH_SET KEY
 		@Override
 		public KEY_TYPE NEXT() {
 			if(!hasNext()) throw new NoSuchElementException();
-			current = next;
+			current = previous = next;
 			next = (int)(links[current]);
-			previous = current;
 			if(index >= 0) index++;
 			return keys[current];
 		}