Implement a scheme-inspired version of cond.

E.g. you group the forms (test and expr) yourself and else is not yet
supported (though you should be able to just put a `(true ...)` in).

clj/macros.clj

(ns macros
  "Dilettante first steps with macros")
(defmacro my-cond [& clauses]
  (when clauses
    `(if ~(ffirst clauses)
       ~(second (first clauses))
       (my-cond ~@(next clauses)))))