TODO: Support for various platforms.
Cosme: Replace 4-space indent with tab indent.
Remove not used properties, which are height and width, from Window.
Return an error value instead of panicing.
Rename window.go to size.go.
Typo: Replace "Sprint" with "Sprintf".
Extract the bar and the percentage as widgets.
Provide customizable progress bar.
Pass the start time to Print methods of each widget.
DONE: Implement customizable progressbar.
Merge branch 'readme/todo'
Merge branch 'feature/customizable'