improved generics so you can pass series as list<Double> for example

...ain/java/com/xeiam/xchart/standalone/RealtimeAttempt.java

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

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

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

...in/java/com/xeiam/xchart/internal/chartpart/AxisPair.java

.../xeiam/xchart/internal/chartpart/PlotContentBarChart.java

...xeiam/xchart/internal/chartpart/PlotContentLineChart.java