Always use latest version of DCL JS library

Now, the DataCamp Light JS library is not baked into the HTML documents in the example, by using self_contained: false. This makes sure that the datacamp light chunks always use the latest version, and the readers can enjoy the latest tweaks and improvements.

Update documentation

v0.4.2

build vignettes

Use knitr hooks instead of hacky wrapper

From now on, tutorial features the go_interactive() function, that you have to add to the top of your R Markdown documents to generate DataCamp Light powered code chunks:

```{r include=FALSE}
tutorial::go_interactive()
```