Make use of the "multiple=True" setting for options that list contributors and repos

[santisoler]

It would be better to pass the list of repositories and list of contributors to be ignored or added by using @click.option(..., multiple=True).

This could break the current interface for the command line interface. After applying these changes, the list of ignored contributors now should be passed as:

collage --extend-ignore contributor-one --extend-ignore contributor-two image.png

References:

• https://click.palletsprojects.com/en/8.1.x/options/#multiple-options