DatesRole: Adding support for relative day parsing

Should address: https://github.com/duckduckgo/zeroclickinfo-goodies/issues/627 and will automagically extend all using the role to support the new stuff!

Supports supacool relative date formats like:

* tomorrow
* today
* now
* yesterday
* last year
* next year
* in a weeks time
* in a month
* in 2 weeks
* 3 months ago

cc @mwmiller 
@mwmiller I don't know the answer to this, do you?