Introduce a new drush_colorize_output() function, to help consistently add color to output text.

[klonos]

This came up in #218:

...perhaps we should introduce a drush_colorize_output($output, $color) function to be re-used in other places?

[serundeputy]

thanks @klonos !
PR: #221

Added a drush_chalk(string $output, string $color) to format pieces of output strings.

I went with drush_chalk because it is not just color it can make text bold and anything you can do with trerminal formatting.

Here is an example:

[serundeputy]

Merged. this will ship w/ 1.4.0.