Coloring

## Issue
The output was colored for dark backgrounds, meaning that there was poor color choice for light colored backgrounds. This fixes Issue #7.

## Solution
Use [argparse][arg] to use a dark background as the default and use `python worldcup.py today --background light` to use a light background.

![screen shot 2014-06-19 at 1 44 14 pm](https://cloud.githubusercontent.com/assets/1320475/3331939/bd32559c-f7e1-11e3-869e-bbc97ad774b3.png)
![screen shot 2014-06-19 at 1 44 09 pm](https://cloud.githubusercontent.com/assets/1320475/3331940/bd35db72-f7e1-11e3-8579-1251c3d1ad23.png)


[arg]:https://docs.python.org/dev/library/argparse.html