Add case_invariant option.

Per: #1

confusables.py

@@ -33,13 +33,16 @@ def __init__(self, confusables_filename):
                 confusables_dict[auth].append(fake)
         self.confusables_dict = confusables_dict
 
-    def expand_char_to_confusables(self, c):
+    def expand_char_to_confusables(self, c, case_invariant=False):
         if c in self.confusables_dict:
-            return '[{}{}]'.format(re.escape(c), re.escape("".join(self.confusables_dict[c])))
+            if case_invariant:
+                return '[{}{}{}]'.format(re.escape(c), re.escape("".join(self.confusables_dict[c.upper()])), ("".join(self.confusables_dict[c.lower()])))
+            else:
+                return '[{}{}]'.format(re.escape(c), re.escape("".join(self.confusables_dict[c])))                
         else:
             return c
 
-    def confusables_regex(self, pattern, letter_test_function=None):
+    def confusables_regex(self, pattern, letter_test_function=None, case_invariant=False):
         """
         Return string with each letter replaced with character class that
         matches the letter and any character that might be confused
@@ -49,7 +52,10 @@ def confusables_regex(self, pattern, letter_test_function=None):
         for c in pattern:
             if ((not letter_test_function) or
                 (letter_test_function and letter_test_function(c))):
-                new += self.expand_char_to_confusables(c)
+                    if case_invariant:
+                        new += self.expand_char_to_confusables(c, case_invariant=case_invariant)
+                    else:
+                        new += self.expand_char_to_confusables(c)                        
             else:
                 new += c
         return new