ETA displayed next to ProgressBar

I also had to change the way the ProgressBar
was printed on the terminal. Previously, the
ProgressBar was printed once, and only the #
characters were added into the line.

Now, the ProgressBar line is reprinted in each
iteration.
Minor formatting fixes to example scripts
Refactored Progress classes. Optimized ProgBar rendering
Merge branch 'progbar-eta' of https://github.com/vape/pyprind into vape-progbar-eta
refactoring into _finish() method, fiix for Python 2.x, and replacing % by format()
more compact print
minor cosmetics
updated documentation