Holocron init command added

This commit adds init command to the holocron's cli. The init command
is meant to be the entry point of the user workflow. It creates an
example blogpost and a very basic _config.yml file in the current
directory.

Fixes #17
Merge pull request #27 from ikalnitsky/command-init

Holocron init command added
Theme style improvements

The commit involves changes:

* color palete - now it's cold, not hot (based on blue)
* styles for tables and blockquotes
* logo contrast was changed
* index page - group by year