Added an ignored_directories option similar to ignore_files to allow for exclusion of directories

Hey there again Domen :smile: 

This pull request implements a similar flag to **ignored_files** called **ignored_directories** which allows you to exclude directories in much the same way as you can files.  I needed this for my current project to exclude the **.git** directory and I'm sure others may find a similar use for it.

Huge credit to Godefroid Chapelle for making my life easy (since most my code is similar to his).

More pull requests to come :smile_cat:  

Cheers
Fotis