Implement string-upcase and document it.

doc/utils.md

@@ -448,6 +448,13 @@ characters of the string.
 Returns a new string with all non-ASCII characters encoded as
 quoted-printable sequences.
 
+    (string-upcase str)
+
+* ```str``` - arbitrary string
+
+Returns the ```str``` with all characters converted to upper case
+using ```char-upcase```. Does not work with UTF-8.
+
 ### Tag
 
     (import util-tag)

src/util-string.scm

@@ -37,6 +37,8 @@
 
   string->qp
 
+  string-upcase
+
   string-tests!
   )
 
@@ -102,6 +104,12 @@
 			    "")))
 		     res)))))
 
+ ;; Returns upper-case version of the string
+ (define (string-upcase str)
+   (list->string
+    (map char-upcase
+	 (string->list str))))
+
  ;; Performs utils module self-tests.
  (define (string-tests!)
    (run-tests
@@ -129,6 +137,9 @@
     (test-equal? string->qp
 		 (string->qp "asdfásdf")
 		 "asdf=c3=a1sdf")
+    (test-equal? string-upcase
+		 (string-upcase "asdFGH")
+		 "ASDFGH")
     ))
 
  )