Merge pull request #1 from royaldark/master

update to latest version
Merge pull request #2 from royaldark/master

update to latest version
Added error handling for nth, although the preconditions don't seem to fire.
Merge https://github.com/Paul-Schliep/clojure-intro-class

Conflicts:
	src/corefns/core.clj
	src/intro/core.clj
Moved turtle tests to a separate file
Added the change of ns to the testing function
Added add-first and add-last functions
Added tests for conact, they require doall
changed errorgui to make it easier to access the dialog later. Tried changing "always on top" to false in invoke-soon, it didn't seem to work.
Merge https://github.com/elenam/clojure-intro-class
A commit to enable push
On mouse-entered the window stops being always on top.
Added duplicate a sequence, need to try it with reduce instead of loop recur