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_001/sol2.py

@@ -1,13 +1,18 @@
 """
-Problem Statement:
+Project Euler Problem 1: https://projecteuler.net/problem=1
+
+Multiples of 3 and 5
+
 If we list all the natural numbers below 10 that are multiples of 3 or 5,
 we get 3, 5, 6 and 9. The sum of these multiples is 23.
-Find the sum of all the multiples of 3 or 5 below N.
+
+Find the sum of all the multiples of 3 or 5 below 1000.
 """
 
 
 def solution(n: int = 1000) -> int:
-    """Returns the sum of all the multiples of 3 or 5 below n.
+    """
+    Returns the sum of all the multiples of 3 or 5 below n.
 
     >>> solution(3)
     0
@@ -30,4 +35,4 @@ def solution(n: int = 1000) -> int:
 
 
 if __name__ == "__main__":
-    print(solution(int(input().strip())))
+    print(f"{solution() = }")