Add optional relation support

[drusellers]

trafficstars

Closes #53

Went through adding optional support by adding a new keyword to the macro has optional. I have not gone through and added all of the matches yet, I wanted to check with the maintainers and see if there was a better suggestion for implementing the macro, but this works today.

[drusellers]

@michiel - are you still maintaining this project? If not I totally understand. Just looking to get a better understanding of what I should expect. Thank you for your work this was a great help to me.