modularize sex

Also rename macros to sex-macros, module-system to sex-modules for
clarity, uniformity, and to avoid name clashes with Chicken's
units/modules named "macros" and "modules"

utils.scm

@@ -1,12 +1,26 @@
-(declare (unit utils))
-
-(include "utils.macros.scm")
-
 (import
+  scheme
+  (chicken base)
   (chicken pathname)
   (chicken process-context)
   srfi-1)
 
+(define-syntax prog1
+  (syntax-rules ()
+    ((prog1 form . forms)
+     (let ((res form))
+       (begin . forms)
+       res))))
+
+(define-syntax with-directory
+  (syntax-rules ()
+    ((with-directory path form . forms)
+     (let ((current-dir (current-directory)))
+       (set-working-directory path)
+       (prog1
+        (begin form . forms)
+        (change-directory current-dir))))))
+
 (define (get-env-var name)
   (get-environment-variable name))