Fixed #55 : DefConceptParser: failed to recognize concept

Fixed #62 : DefConceptParser: parsing error
Fixed #64 : DefConceptParser: Failed to parse when too many concept keyword
Fixed #65 : DefConceptParser : Add auto_eval keyword
Fixed #66 : DefConceptParser : Add def_var keyword
Fixed #67 : Add get_errors()

src/core/utils.py

@@ -645,8 +645,11 @@ def flatten_all_children(item, get_children):
 def flatten(list_of_lists):
     """
     Flatten an list containing other lists
+    https://stackoverflow.com/questions/952914/how-to-make-a-flat-list-out-of-a-list-of-lists?page=1&tab=votes#tab-top
     """
-    return [item for sublist in list_of_lists for item in sublist]
+    import functools
+    import operator
+    return functools.reduce(operator.iconcat, list_of_lists, [])
 
 
 def get_text_from_tokens(tokens, custom_switcher=None, tracker=None):