Expose gitignore status to custom colorization via EXA_COLORS

[cohml]

The exa website clearly indicates that it is possible to override the default colors of the following output components:

• ga New
• gm Modified
• gd Deleted
• gv Renamed
• gt Type change

However, Ignored is strangely absent.

If it is currently possible to control the color of that I, please update the site with the requisite instructions.

Otherwise, if it is not currently possible, adding this ability would be much appreciated. It seems like an odd oversight, given that every other major git status can be customized.