Merge branch 'master' into polygon_polyline

# Conflicts:
#	Sources/QuartzRenderer/QuartzRenderer.swift
#	Sources/SVGRenderer/SVGRenderer.swift
#	Sources/SwiftPlot/BarChart.swift
#	Sources/SwiftPlot/GraphLayout.swift
#	Sources/SwiftPlot/Histogram.swift
#	Sources/SwiftPlot/LineChart.swift
#	Sources/SwiftPlot/ScatterChart.swift
#	Tests/SwiftPlotTests/Reference/quartz/_01_single_series_line_chart.png
#	Tests/SwiftPlotTests/Reference/quartz/_02_multiple_series_line_chart.png
#	Tests/SwiftPlotTests/Reference/quartz/_03_sub_plot_horizontally_stacked_line_chart.png
#	Tests/SwiftPlotTests/Reference/quartz/_04_sub_plot_vertically_stacked_line_chart.png
#	Tests/SwiftPlotTests/Reference/quartz/_06_function_plot_line_chart.png
#	Tests/SwiftPlotTests/Reference/quartz/_07_secondary_axis_line_chart.png
#	Tests/SwiftPlotTests/Reference/quartz/_27_histogram_multi_stacked_step.png
#	Tests/SwiftPlotTests/Reference/quartz/_reg_57_histogram_stacked_step_offset.png

Author: odmir

.github/workflows/swift.yml

@@ -17,4 +17,10 @@ jobs:
     - name: Build
       run: swift build -v
     - name: Run tests
-      run: swift test -v
+      run: SWIFTPLOT_TEST_OUTPUT=/private/var/tmp/swiftplot swift test -v
+    - name: Upload test artefacts
+      uses: actions/upload-artifact@v1
+      if: always()
+      with:
+        name: images
+        path: /private/var/tmp/swiftplot/