bring gemfile up-to-date

the gem source needed to be more secure, there needed to be an explicit
ruby version, and I'm not actually using sinatra-subdomain.
organize class mess a bit

along with multiple sections comes multiple directories for
organization. blog posts have been moved under /blog and I've extracted
the renderer to a general Site::Renderer
explicitly filter out dot-files when building animation list

I initially just chopped off the first two entries in the directory
assuming they would be "." and "..", but this won't necessarily be true
for other filesystems. I could have explicity sorted the entries and
stuck with the same method but I've opted to just filter out all entries
that start with a '.'