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.module.scm

@@ -0,0 +1,10 @@
+(module utils
+    (get-env-var
+     set-working-directory
+     to-absolute-pathname
+     list-split
+     list-join
+     recons
+     with-directory
+     )
+  "utils.scm")