Added the ability to ignore duplicates, it just skips them without throwing an error, makes the importer a bit more forgiving.

Conflicts:
	README.markdown
	src/app/code/community/AvS/FastSimpleImport/Model/Import/Entity/Category.php
[~BUGFIX] Cleaned up the merge
Merge pull request #65 from ho-nl/ignore-duplicates

Added the ability to ignore duplicate categories, it just skips them without throwing an error, makes the importer a bit more forgiving.