updates progress-tracker and adds test.

There was a bug in my code regarding time interpretation.
This commit adresses it so that this feature does not fail with old postcast entries with a different time format.
Also, as this issue bug could be easily perceived if we had tests, this commit add some basic tests for the utilitary methods used.

fixes #57
Merge pull request #60 from cirocosta/bug/progress-tracker

(Issue 57) - Fix problema progress-tracker formatação