Rename Project Euler directories and other dependent changes (#3300)

* Rename all Project Euler directories:

Reason:
The change was done to maintain consistency throughout the directory
and to keep all directories in sorted order.

Due to the above change, some config files had to be modified:
'problem_22` -> `problem_022`

* Update scripts to pad zeroes in PE directories

project_euler/problem_012/sol2.py

@@ -0,0 +1,47 @@
+"""
+Highly divisible triangular numbers
+Problem 12
+The sequence of triangle numbers is generated by adding the natural numbers. So
+the 7th triangle number would be 1 + 2 + 3 + 4 + 5 + 6 + 7 = 28. The first ten
+terms would be:
+
+1, 3, 6, 10, 15, 21, 28, 36, 45, 55, ...
+
+Let us list the factors of the first seven triangle numbers:
+
+ 1: 1
+ 3: 1,3
+ 6: 1,2,3,6
+10: 1,2,5,10
+15: 1,3,5,15
+21: 1,3,7,21
+28: 1,2,4,7,14,28
+We can see that 28 is the first triangle number to have over five divisors.
+
+What is the value of the first triangle number to have over five hundred
+divisors?
+"""
+
+
+def triangle_number_generator():
+    for n in range(1, 1000000):
+        yield n * (n + 1) // 2
+
+
+def count_divisors(n):
+    return sum([2 for i in range(1, int(n ** 0.5) + 1) if n % i == 0 and i * i != n])
+
+
+def solution():
+    """Returns the value of the first triangle number to have over five hundred
+    divisors.
+
+    # The code below has been commented due to slow execution affecting Travis.
+    # >>> solution()
+    # 76576500
+    """
+    return next(i for i in triangle_number_generator() if count_divisors(i) > 500)
+
+
+if __name__ == "__main__":
+    print(solution())