Use os.path.join() to create paths vs. strings

[humphd]

Instead of creating paths out of strings, do it in a cross-platform way with os.path.join(), for example: https://github.com/lmpham1/cool_ssg_generator/blob/master/helper.py#L15

[lmpham1]

I was struggling a bit with figuring out "/" and "" in the pathing. I have changed most of the code that needs pathing to use os.path.join() and other os.path functions with the commit 169195d