This library provides a text mode progressbar. This is typically
used to display the progress of a long running operation, providing a
visual clue that processing is underway.

The ProgressBar class manages the progress, and the format of the
line is given by a number of widgets. A widget is an object that
may display diferently depending on the state of the progress. There
are three types of widget: - a string, which always shows itself; -
a ProgressBarWidget, which may return a diferent value every time it's
update method is called; and - a ProgressBarWidgetHFill, which is like
ProgressBarWidget, except it expands to fill the remaining width of
the line.

The progressbar module is very easy to use, yet very powerful. And
automatically supports features like auto-resizing when available.
