Added an option to set foreground color at runtime.

-c or --color [0-7]

Code change to implement this feature:
- Added getopt parsing in main.
- Added a usage() function to print usage.
- FG_COLOR is now DEFAULT_FG_COLOR
- The default color name has a new define, DEFAULT_FG_COLOR_NAME
Merge pull request #1 from dereckson/master

Set foreground color as program option.