Document various things

[jens1o]

• Code style -> CONTRIBUTING.md
• things to notice before creating an issue -> CONTRIBUTING.md
• On what do I look when accepting prs/issues? -> CONTRIBUTING.md
• When it's allowed to push things up -> CONTRIBUTING.md
• Rules for the behaviour of the users(including me) -> CONTRIBUTING.md
• How much time I spend on the project -> README.md
• Vision -> VISION.md
• Issue template -> .github/ISSUE_TEMPLATE.md
• Pull Request template -> .github/PULL_REQUEST_TEMPLATE.md

// add other things...

[jens1o]

I'm going to do this after class tests... or when I'd like to.

With release of 0.9, this should be closed.

[jens1o]

Time spending: c0c3aff and 21130eb

[jens1o]

eacb83c