Use scsh-process Chicken egg

As advised by Vasilij on IRC. This is thread-safe, whereas (chicken
process) gives mysterious failures in every batch of documents I
tried.

TODO: Rethink `pandoc-command-line`.

pandoc.chicken.scm

@@ -11,10 +11,10 @@
           (only (chicken io) read-byte write-byte)
           (only (chicken port) copy-port)
           (only (chicken process) process process-wait)
-          (rename (only (medea) read-json)
-                  (read-json json-read)))
+          (only (scsh-process) run/port)
+          (only (medea) read-json))
 
-  (define (run-read-write args input-port read-output)
+  (define (run-read-write/old args input-port read-output)
     (receive (from-sub to-sub sub) (process (car args) (cdr args))
       (copy-port input-port to-sub read-byte write-byte)
       (close-output-port to-sub)
@@ -28,6 +28,11 @@
           (if (and clean-exit? (eqv? 0 exit-status)) output
               (error "Error running" args))))))
 
+  (define (pandoc-port->json input-format input-port)
+    (let ((pandoc (string->symbol (car (pandoc-command-line)))))
+      (read-json (run/port (,pandoc --from ,input-format --to json)
+                           (= 0 input-port)))))
+
   (define (call-with-binary-input-file filename proc)
     (let ((port (open-input-file filename #:binary)))
       (dynamic-wind (lambda () #f)

pandoc.r5rs.scm

@@ -100,13 +100,6 @@
   (assert-supported-version)
   (convert-many (vector->list (cdr (assq 'blocks json)))))
 
-(define (pandoc-port->json input-format input-port)
-  (run-read-write (append (pandoc-command-line)
-                          (list "--from" (symbol->string input-format)
-                                "--to" "json"))
-                  input-port
-                  json-read))
-
 (define (pandoc-port->sxml input-format input-port)
   (pandoc-json->sxml (pandoc-port->json input-format input-port)))