Add support for the role attibute

[jpminnovation]

Would it be possible to support a role attribute for the graphs, so that using CSS, we can customize some of its properties (such as alignment, width, etc ...) ?

Something such as :

class="chartjs"

[ggrossetie]

We could add a default role but it should also be possible to define custom roles using the role attribute:

chart::sample-data.csv[line,engine="chartjs",role="sample,data,line-chart"]

[jpminnovation]

Perfect