added percentage, percentage bar, updated screenshot. 

Percentage bars!

![screenshot](https://f.cloud.github.com/assets/51505/1449228/035a6ee8-4265-11e3-89bd-58eccf05bf8d.png)

The max bar width is 40% of the screen width, that was easier to calculate than to figure out the maximum available space with the table columns.

*Also in this PR*

* right aligned the time to make it easier to read.
* fixed what I assumed to be a bug that lead to last task to always be included even if it was less than 20ms.
* moved `20` to `var MIN_DIFF` (minimum diff milliseconds) so it can easily become a user option.