area charts

...-demo/src/main/java/com/xeiam/xchart/demo/XChartDemo.java

...n/java/com/xeiam/xchart/demo/charts/area/AreaChart01.java

...n/java/com/xeiam/xchart/demo/charts/line/LineChart01.java

...n/java/com/xeiam/xchart/demo/charts/line/LineChart04.java

.../com/xeiam/xchart/demo/charts/scatter/ScatterChart01.java

xchart/src/main/java/com/xeiam/xchart/AreaChart.java

xchart/src/main/java/com/xeiam/xchart/ChartBuilder.java

...java/com/xeiam/xchart/internal/chartpart/PlotContent.java

xchart/src/main/java/com/xeiam/xchart/style/SeriesColor.java