Actually run test cases in test/conditions.lisp

* test/conditions.lisp (define-condition-suite): generate unique names
  for test cases; placing them in different test suites is not enough
Made link part of reference-spec optional in src/types.lisp

* src/types.lisp (header): updated copyright
  (reference-spec): made link part optional as stated in documentation
  string
* src/conditions.lisp (print-reference): added type declaration for
  spec parameter
Added explanatory comment in condition-references in src/conditions.lisp

* src/conditions.lisp (condition-references chainable-condition):
  added a comment explaining precedence of references