* Arc with rounded ends implementation
* End style option
* Working border radius implementation for arcs
* Linting
* Fix bug introduced when converting to new border object
* Fix bugs identified by tests
* Arc border radius tests
* Add test to cover small borderRadii
* Reduce the weight of the arc border implementation
* lint fix
Add functionality to give pie & doughnut datasets a weight attribute, which affects the relative thickness of the dataset when there are multiple datasets in pie & doughnut charts. The default weight of each dataset is 1, providing any other numerical value will allow the pie or doughnut dataset to be drawn with a thickness relative to its default size.
For example a weight of 2 will allow the dataset to be drawn double its typical dataset thickness. Note that the weight attribute will only affect a pie or doughnut chart if there is more than one visible dataset. Using weight on a pie or doughnut dataset when there is only one dataset on the chart will have no affect.
