Merge pull request #5 from Paul-Schliep/master

Merging recent changes
commit before a merge
Merge branch 'master' of git://github.com/royaldark/clojure-intro-class
added a number to best-approximation, tested in repl
added a few more types
Added error handling for stack interface.
added interfaces for Associative and Reversible, tested, but didn't retest previous messages
Added message for "sorted"
added a type for sequential, but cannot test it since I don't know what uses it :-(
First step towards handling compilation errors. Put code in student.clj, run (erun) at repl.
added a couple more compilation errors
Added group-a-seq