Add smooth option to series
Support same subtypes in chart_line as in chart_scatter
Added tests for smoothed charts.
Additional test for smoothed charts.
Changes for smooth scatter and line plots
PEP8 formatting changes
Add comment
Remove subtype stuff for line charts
Add note about smooth option in add_series docs
Merge pull request #22 from dieterv77/SmoothLineCharts

Subtypes for line charts