Significantly better memory performance (Thanks @drslump!)

Added __slots__ to RulePtr and Token, resulting in significantly lower memory consumption.

As suggested by @drslump.

lark/lexer.py

@@ -25,6 +25,8 @@ class UnexpectedInput(LexError):
         self.considered_rules = considered_rules
 
 class Token(Str):
+    __slots__ = ('type', 'pos_in_stream', 'value', 'line', 'column', 'end_line', 'end_column')
+
     def __new__(cls, type_, value, pos_in_stream=None, line=None, column=None):
         self = super(Token, cls).__new__(cls, value)
         self.type = type_

lark/parsers/grammar_analysis.py

@@ -5,6 +5,8 @@ from ..grammar import Rule
 
 
 class RulePtr(object):
+    __slots__ = ('rule', 'index')
+
     def __init__(self, rule, index):
         assert isinstance(rule, Rule)
         assert index <= len(rule.expansion)