Data controllers should now rarely implement addElements and addElementAndReset but instead should define dataElementType (and optionally datasetElementType). Also remove some dead code (e.g. numBars, colorForNewElement, etc.).
Updated all chart types to use the helper.getHoverColor. Pattern fills can now be specified for both fill and line portions of a chart. Updates chartjs/Chart.js#1323
Meta info are now scoped by chart and moved under the dataset._meta map { chart.id -> meta }. Meta for a specific chart (and dataset) can be accessed using chart.getDatasetMeta(datasetIndex) or from the dataset controller using getMeta(). Note that helpers.uid() now generates an int (instead of a string) to make lookups in the _meta map faster.
