Added support for negative variables in the tokenizer and ptoken object.

ptoken.py

@@ -1,7 +1,8 @@
 class Token:
-	def __init__(self, value, type):
+	def __init__(self, value, type, is_negative_variable = False):
 		self.value = value
 		self.type = type
+		self.is_negative_variable = is_negative_variable
 
 class TokenType:
 	add = 0