Merge pull request #1 from royaldark/master

Pull
Added draw-polygon, not quite done however and started some additional core functions
Merge branch 'master' of https://github.com/Paul-Schliep/clojure-intro-class

Conflicts:
	src/corefns/core.clj
	src/intro/core.clj
Added draw-polygon to intro class and added additional
(NullPointerException) to the error message associated with that.
Added draw-spiral to clojure intro class
Merge https://github.com/royaldark/clojure-intro-class
Added versions 2 and 3 of draw-spiral; still in works
Merge https://github.com/Paul-Schliep/clojure-intro-class

Conflicts:
	src/corefns/core.clj
	src/intro/core.clj