Add a method for adding custom CSS class

Allow us to append a class for the body when it's the night
Merge pull request #11 from LeoColomb/patch-1

Add a method for adding custom CSS class
Update README.md
Merge pull request #12 from LeoColomb/patch-2

Update README.md
Bump version, fixes some lint issues, and ready to go!

Bumped to v0.2 since some API changes and hard script variations.