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 prefer ```shutil.copytree``` too, but  this method requires that the destination directory doesn't exist. But our workflow assumes, that the user creates directory and then run ```init``` to create a skeleton. 
I couldn't find the workaround to handle this issue, and didn't want to write my own bicycle for that, that's why I decided to use ```distutils```. Can you suggest some other approach?