Ability to pause and resume the progressbar

[hrj]

In our test harness, we allow execution of the tests to be paused and then, continued at a later time.

It would be great if the progress bar can be paused and resumed (I think it used to work fine before the multi-threaded version).

[ctongfei]

Pause/resume was never implemented in the single-threaded version: the estimated time remaining needs to be recomputed while taking into account of the timespan paused.

[ctongfei]

Fixed in 0.9.0: There are pause and resume methods in ProgressBars.