Fix style of the first ten solutions for Project Euler (#3242)

* Fix style of the first ten solutions for Project Euler

- Unify the header docstring, and add reference URLs to wikipedia
  or similar
- Fix docstrings to be properly multilined
- Add newlines where appropriate
- Add doctests where they were missing
- Remove doctests that test for the correct solution
- fix obvious spelling or grammar mistakes in comments and
  exception messages
- Fix line endings to be UNIX. This makes two of the files seem
  to have changed completely
- no functional changes in any of the solutions were done
  (except for the spelling fixes mentioned above)

* Fix docstrings and main function as per Style Guide

project_euler/problem_006/sol1.py

@@ -1,22 +1,25 @@
 """
-Problem 6: https://projecteuler.net/problem=6
+Project Euler Problem 6: https://projecteuler.net/problem=6
+
+Sum square difference
 
 The sum of the squares of the first ten natural numbers is,
-            1^2 + 2^2 + ... + 10^2 = 385
+    1^2 + 2^2 + ... + 10^2 = 385
 
 The square of the sum of the first ten natural numbers is,
-            (1 + 2 + ... + 10)^2 = 552 = 3025
+    (1 + 2 + ... + 10)^2 = 55^2 = 3025
 
-Hence the difference between the sum of the squares of the first ten natural
-numbers and the square of the sum is 3025 − 385 = 2640.
+Hence the difference between the sum of the squares of the first ten
+natural numbers and the square of the sum is 3025 - 385 = 2640.
 
-Find the difference between the sum of the squares of the first N natural
-numbers and the square of the sum.
+Find the difference between the sum of the squares of the first one
+hundred natural numbers and the square of the sum.
 """
 
 
 def solution(n: int = 100) -> int:
-    """Returns the difference between the sum of the squares of the first n
+    """
+    Returns the difference between the sum of the squares of the first n
     natural numbers and the square of the sum.
 
     >>> solution(10)
@@ -27,9 +30,8 @@ def solution(n: int = 100) -> int:
     41230
     >>> solution(50)
     1582700
-    >>> solution()
-    25164150
     """
+
     sum_of_squares = 0
     sum_of_ints = 0
     for i in range(1, n + 1):
@@ -39,7 +41,4 @@ def solution(n: int = 100) -> int:
 
 
 if __name__ == "__main__":
-    import doctest
-
-    doctest.testmod()
-    print(solution(int(input().strip())))
+    print(f"{solution() = }")