Add support for archive pages

[benniemosher]

Solves #8 and #24

Can be demoed at https://benniemosher.com

[samarsault]

Woudn't it be better if instead of the user creating the category.html file, it is included by default ?

[benniemosher]

@thelehhman I tried putting it in the theme, but then when you try and go to /categories/#Learning it returns a 404. I put the categories.html in my personal site repo and it renders just fine. I can't figure out why that is or how to fix it. Thoughts?

[samarsault]

Okay it looks great!

Before merging however, please account for the following

1. Update your base branch to include the latest version fix jekyll v3.8.6 #24
2. Don't increment version number. Keep it at 0.9. It's yet to be released
3. Rebase all the commits into 2-3 commits max.

Thank you :)

[benniemosher]

Created a new PR with an updated base project. This should allow me to rebase off of upstream easier later. #31