unify variant types and records; also make-foo instead of <foo>

* module/system/base/syntax.scm (define-record): Rework to separate the
  type and its constructor. Now (define-record (<foo> bar)) will create
  `make-foo' as the constructor, not `<foo>'. Also the constructor now
  takes either keyword or positional arguments, so that it can be used as
  the implementation of variant types as well.
  (|): Map directly to define-record instead of rolling our own thing.

* module/language/scheme/translate.scm:
* module/system/base/language.scm:
* module/system/il/compile.scm:
* module/system/il/ghil.scm:
* module/system/il/glil.scm:
* module/system/repl/common.scm:
* module/system/vm/assemble.scm:
* module/system/vm/debug.scm: Change instances of record creation to use
  the make-foo procedures instead of <foo>. Adjust module exports as
  necessary.

module/system/base/language.scm

@@ -36,7 +36,7 @@
 			   ))
 
 (define-macro (define-language name . spec)
-  `(define ,name (,<language> :name ',name ,@spec)))
+  `(define ,name (,make-language :name ',name ,@spec)))
 
 (define (lookup-language name)
   (let ((m (resolve-module `(language ,name spec))))