Add style improvements to solutions for Project Euler Problem 04 (#2945)

* Fix typehints in project_euler/problem01

Squashed commit of the following:

commit 6801d073b31bf702814861cd3b07b634ca295bfa
Author: Archaengel <god11341258@gmail.com>
Date:   Mon Oct 5 16:40:10 2020 -0700

    Fix typehints in project_euler/problem01

commit 29afc3af114abd1b99dc3f7c8fc99128229db131
Author: Archaengel <god11341258@gmail.com>
Date:   Mon Oct 5 15:06:34 2020 -0700

    Add typehints and default argument for project_euler/problem_01

* Add default args, typehints, and expand variable names for PE prob 02

* Add style improvements for first solution of PE Problem 02

* Add default arg and typehints for second solution of PE Problem 02

* Add default arg for third solution of PE Problem 02

* Add style improvements for 1st soln of PE problem 03

* Add default arg and typehints for 2nd soln of PE problem 03

* Add default arg for 3rd soln of PE problem 03

* Remove unnecessary newlines

* Remove unnecessary newlines

* Fix end of file for 2nd soln in PE problem 03

* Add style improvements to solutions for PE problem 04

* Restore original newlines in soln for PE problem 04

* Fix punctuation in docstring for PE problem 04

* Restore solution bodies for PE problem 04

* Expand variable names for 2nd soln of PE problem 04