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
I'd prefer to use `shutil.copytree` instead, since the purpose of `distutils` module is distribution and it's a bit obsolete, so I don't know about its future.