DirectoryEntryReference: implement chapter 3.2.6
This commit adds in the implementation for RFC5545's chapter 3.2.6. Moving forward, there are two TODO's that should be considered: 1. When the CAL-ADDRESS type is implemented, there needs to be something added to this and other classes like it that enforce the restriction on which content line types are allowed to possess this parameter type. 2. When this project is able to be ported over in such a way that it can be browser packaged, there might be an issue with using the NodeJS implemented URL class. I'm not sure about if it will work or not, but future me looking at git blames for why it is not working should take some direction from this message. Keep going, future me, keep going! Signed-off-by: Mark Stenglein <mark@stengle.in>