-Add a better description on main page (in site.yaml) (Fixes #113)

-Replace all instances of the word "quarter" with "semester" (Fixes #140)
-Move "Learn more" button from about page to main page and link to syllabus (previously went nowhere)
-Add better description on about page
-Move about page to end of navigation row (it's less important than the other pages)
-Update course number to be correct
-Update my yaml file with final links and updated feed, including bonus lightning talks and hackathons

I went through my blog and switched from using a category to using a tag for posts I made for this class. I also added my missing links and assignments, though some of the blog posts have existed for a while. I apologize for the delay in this pull request.