Configurable blog

[RaphaelPour]

Introduce blog config that contains information like author, domain and all other details that are currently hardcoded about myself in order to make blogctl usable by others.

Something like:

{
  "version": 1,
  "author": "Raphael",
  "domain": "evilcookie.de",
  "description": "Hi, I'm Raphael. I write about my software developer journey. You can find my stuff on [github](https://github.com/RaphaelPour)."
  "footer":"[RSS](https://evilcookie.de/rss.xml)|[Impressum](https://evilcookie.de/impressum.html)"
}