Handle CRLF and Unicode line endings in read-line

* libguile/rdelim.c (scm_read_line): handle CRLF, LS and PS
* module/ice-9/suspendable-ports.scm (read-line): handle CRLF, LS, and PS
* module/web/http.scm (read-header-line): take advantage of CRLF in read-line
   (read-header): don't need to test for \return
* test-suite/tests/rdelim.test: new tests for read-line CRLF, LS and PS
* doc/ref/api-io.texi: update doc for read-line

module/web/http.scm

@@ -157,13 +157,12 @@ The default writer will call ‘put-string’."
 Raise a 'bad-header' exception if the line does not end in CRLF or LF,
 or if EOF is reached."
   (match (%read-line port)
+    (((? string? line) . "\r\n")
+     line)
     (((? string? line) . #\newline)
-     ;; '%read-line' does not consider #\return a delimiter; so if it's
-     ;; there, remove it.  We are more tolerant than the RFC in that we
-     ;; tolerate LF-only endings.
-     (if (string-suffix? "\r" line)
-         (string-drop-right line 1)
-         line))
+     ;; We are more tolerant than the RFC in that we tolerate LF-only
+     ;; endings.
+     line)
     ((line . _)                                ;EOF or missing delimiter
      (bad-header 'read-header-line line))))
 
@@ -184,8 +183,7 @@ was known but the value was invalid.
 Returns the end-of-file object for both values if the end of the message
 body was reached (i.e., a blank line)."
   (let ((line (read-header-line port)))
-    (if (or (string-null? line)
-            (string=? line "\r"))
+    (if (string-null? line)
         (values *eof* *eof*)
         (let* ((delim (or (string-index line #\:)
                           (bad-header '%read line)))