Add Jekyll to the Gemfile
Add a stub for an archive generator plugin

Current functionality:

- Create a hash of months to their respective posts
Add a working ArchivePage class
Stop printing months and titles to the console
Clean up ArchivePage implementation

Replace the hash of months and corresponding posts with a simple
(reverse) iteration over site.posts
Remove 'base' from ArchivePage#initialize params
Skip linklog posts on the archive page
Add a linklog generator

Code has been shamelessly copied from archive_generator.rb and will be
refactored shortly.
Refactor ArchivePage into its own file
Create an ArticleArchive class

ArticleArchive is a subclass of ArchivePage. It overrides #should_skip?
to indicate that linklog posts should be skipped.
Create a LinklogArchive class

Like ArticleArchive, LinklogArchive is a subclass of ArchivePage. It
overrides #should_skip? to indicate that ordinary articles should be
skipped.
Move linklog generation to archive_generator.rb

No sense in having two separate generator classes for ordinary articles
and linklogs.