Support gauge chart

[shali3]

Hi there,
I really like this library but I wanted to use it for a gauge chart and there was no nice way to do it so I'm suggesting a change to the library (non-breaking).

In order to get what I wanted I basically needed a doughnut chart that started at -90deg and the total values were represented in half the circle.
I added these 2 properties to the doughnut chart and created an example with a gauge chart.

I hope you like my changes and happy to get your feedback.

[etimberg]

Related to #524 since a start angle setting is needed

[etimberg]

Done in v2 in #2271