Pull in AdaptiveETA change

The change was originally done here (not by me):

https://code.google.com/p/python-progressbar/source/detail?r=68c8889525476803ee5c9c880e00e3c8d8341dae
Add a gitignore

+ Add standard gitignore from here:
https://github.com/github/gitignore/blob/master/Python.gitignore
Merge pull request #9 from alapidas/master

Add AdaptiveETA code from original python-progressbar