[2018] Remove Python 2.7 support (#58)

* [2018] Remove Python 2.7 support

* Fix readme

Author: kfarnung

2018/README.md

@@ -5,7 +5,7 @@ https://adventofcode.com/2018
 ## Language
 
 This year I chose to implement in Python 2, but ported the code such that it
-works in either Python 2 or Python 3.
+works properly in Python 3. Python 2 support has been removed.
 
 ## Preparation
 

2018/day01/day01.py

@@ -4,8 +4,6 @@
 https://adventofcode.com/2018/day/1
 """
 
-from __future__ import print_function
-
 from functools import reduce
 
 

2018/day02/day02.py

@@ -4,8 +4,6 @@
 https://adventofcode.com/2018/day/2
 """
 
-from __future__ import print_function
-
 from collections import Counter, defaultdict
 from functools import reduce
 

2018/day03/day03.py

@@ -4,8 +4,6 @@
 https://adventofcode.com/2018/day/3
 """
 
-from __future__ import print_function
-
 import re
 from collections import defaultdict
 from functools import reduce

2018/day04/day04.py

@@ -4,8 +4,6 @@
 https://adventofcode.com/2018/day/4
 """
 
-from __future__ import print_function
-
 import re
 from collections import defaultdict
 

2018/day05/day05.py

@@ -4,8 +4,6 @@
 https://adventofcode.com/2018/day/5
 """
 
-from __future__ import print_function
-
 from string import ascii_lowercase
 
 

2018/day06/day06.py

@@ -4,13 +4,9 @@
 https://adventofcode.com/2018/day/6
 """
 
-from __future__ import print_function
-
 import sys
 from functools import reduce
 
-_MIN_INT = -sys.maxsize - 1
-
 
 class Point:
     """Represents a point in 2D space."""
@@ -37,10 +33,10 @@ class Rect:
     @staticmethod
     def bounding_box(points):
         """Returns a rectangle which forms the boundary of all points"""
-        min_x = sys.maxsize
-        min_y = sys.maxsize
-        max_x = _MIN_INT
-        max_y = _MIN_INT
+        min_x = float('inf')
+        min_y = float('inf')
+        max_x = float('-inf')
+        max_y = float('-inf')
 
         for point in points:
             min_x = min(min_x, point.coord_x)

2018/day07/day07.py

@@ -4,8 +4,6 @@
 https://adventofcode.com/2018/day/7
 """
 
-from __future__ import print_function
-
 import re
 from collections import defaultdict
 

2018/day08/day08.py

@@ -4,8 +4,6 @@
 https://adventofcode.com/2018/day/8
 """
 
-from __future__ import print_function
-
 
 class TreeNode:  # pylint: disable=too-few-public-methods
     """Represents a single node in the tree."""

2018/day09/day09.py

@@ -4,8 +4,6 @@
 https://adventofcode.com/2018/day/9
 """
 
-from __future__ import print_function
-
 import re
 from collections import defaultdict