Fixed #101 : Implement PLURIAL

Fixed #103 : Implement PlurialNodeParser
Fixed #104 : Implement dynamic concept
Fixed #107 : PrepareEvalxxxEvaluator: context hints are lost on a second evaluation

sheerka_backup/default.sb

@@ -53,9 +53,6 @@ woman is a human
 girl is a female
 girl is a human
 
-
-def concept boys
-def concept girls
 def concept shirt
 def concept table
 
@@ -75,4 +72,8 @@ def concept what is the x of y pre is_question() where x is an adjective as smar
 
 #
 def concept he ret memory("self is a human and self is a male")
-def concept she ret memory("self is a human and self is a female")
+def concept she ret memory("self is a human and self is a female")
+
+#
+def concept sky
+def concept gender