Use pre-commit

[pre-commit](https://pre-commit.com/) automatically runs tools like
linters and fixers to make development easier. This change adds a simple
pre-commit config file with an example trailing whitespace fixer and
applies it to the existing project.

Additionally, don't ignore the lib directory (an error introduced in #8).

static/css/main.css

@@ -25,7 +25,7 @@ body{
     font-size: 25px;
     text-align: start;
 }
-.shadow{ 
+.shadow{
     text-shadow: #4c5c68 -5px 3px 5px;
 }
 .app_subhdr{
@@ -61,7 +61,7 @@ body{
     grid-area: right_col
 }
 .python_logo{
-    
+
 }
 #python_logo{
     height: 50px;