added make-module-language-tag and use it and make-section-tag

in a few places

original commit: 353da62843a2b976e300fdd37abdd9b6d6c4894a

collects/scribble/tag.rkt

@@ -14,6 +14,7 @@
                       #:tag-prefixes (or/c #f (listof string?)))
                      . ->* .
                      tag?)]
+  [make-module-language-tag (-> symbol? tag?)]
   [taglet? (any/c . -> . boolean?)]
   [module-path-prefix->string (module-path? . -> . string?)]
   [module-path-index->taglet (module-path-index? . -> . taglet?)]
@@ -25,6 +26,9 @@
 (define (make-section-tag s #:doc [doc #f] #:tag-prefixes [prefix #f])
   `(part ,(doc-prefix doc prefix s)))
 
+(define (make-module-language-tag langname)
+  `(mod-path ,(symbol->string langname)))
+
 (define (taglet? v)
   (and (not (generated-tag? v))
        (tag? (list 'something v))))

collects/scribblings/scribble/tag.scrbl

@@ -26,6 +26,11 @@ references a section in the document implemented by
 prefixes (for intermediate sections, typically) can be provided as
 @racket[tag-prefixes].}
 
+@defproc[(make-module-language-tag [lang symbol?]) tag?]{
+  Forms a @tech{tag} that refers to a section 
+  that contains @racket[defmodulelang] for the language
+  @racket[lang].
+}
 
 @defproc[(taglet? [v any/c]) boolean?]{