Provide a dictionary interface inside of templates

[Abbe98]

Dicts would be very useful to many Snowman users as it's easy to sterilize to JSON as well as allow one to return multiply values from a template, we should therefore implement a basic dict interface.

Maybe a more basic implementation of the Sprig one or even introduce Sprig as a dependency?

https://github.com/Masterminds/sprig/blob/master/dict.go