Reestructure CairoPlot source code to make it a python package

Since cairoplot is growing up, it would be nice to prevent modules being overwritten by others softwares. The name Series, for example, is really commom and can cause some name confict with other modules.

Nevertheless Series is a part of CairoPlot, but is currently treated as a module apart during the installation process.

For more details check the specification link.