Roadmapper

* Fixed SVG output not showing vertical line.

* Fixed [69](https://github.com/csgoh/roadmapper/issues/69). Task bar was not displayed with the correct width.
* Fixed defect that was introduced with the fixed for [61](https://github.com/csgoh/roadmapper/issues/61)

* Fixed [61](https://github.com/csgoh/roadmapper/issues/61). Incorrect Group box height due to multiple milestones.

- Fixed 39 Hardcoded text alignment issue
- Added set_background_colour() method. You can now change background colour.
- Added "svg" as a painter type. You can now save the diagram as svg file. You just have to set `painter_type = "svg"` when creating the Roadmap.

- Removed the dependency of Arial font on Linux system. i.e. The following commands to install MSCoreFonts is no longer required.
- sudo apt install ttf-mscorefonts-installer
- sudo fc-cache -f
- Code clean up

- Fixed [20](https://github.com/csgoh/roadmapper/issues/20): Removed absolute font naming dependency. i.e. "arial.ttf"
- Fixed [22](https://github.com/csgoh/roadmapper/issues/22): The date argument for add_timeline() method is now passed as keyword argument. e.g. add_timeline(start="2023-05-16")
- Introduced the 'with' statement for context management to create cleaner code.