[WIP] Add better unit tests for core functions

This pull requests replaces my hacky `sasstest` module with [bootcamp](http://thejameskyle.com/bootcamp/).

Having good test coverages is a prereq. for the refactors I have planned for core.

Unit test:
- [ ] lazy
- [ ] is-lazy (should be private)
- [ ] exec-lazy (maybe not possible)
- [x] get
- [x] set
- [x] set-default
- [ ] looks-like-an-alias (should be private)
- [x] resolve-alias
- [x] resolve-aliases
- [x] lookup
- [x] implode
- [x] map-merge-recursive