Fixed minor error in README.org

* README.org (Introduction): primarily {unreadably -> unreadable}
  printing
Improved print-object method in src/protocol.lisp

* src/protocol.lisp (print-object print-items-mixin): force one space
  after type name except when there are no print items
* test/protocol.lisp (mock): new class; mock class for tests
  (print-items append mock): new method; behavior for mock class
  (test print-items-mixin.smoke): new test; test integration of
  `print-items-mixin' and `print-object'