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"

sex-macros.scm

@@ -1,11 +1,11 @@
-(declare (unit sex-macros))
-
 (import
+  scheme
+  (only fmt fmt)
+  (chicken base)
   (chicken plist)
   (chicken string))
 
 (define (cat-syms s-1 s-2)
-  (import fmt)
   (fmt #f s-1 s-2))
 
 (define (cat sym-1 sym-2)
@@ -14,18 +14,20 @@
 (define (register-macro name arglist body)
   (put! name 'sex-macro
         `(lambda ,arglist
+           (import scheme
+                   (only sex-macros cat))
            ,@body)))
 
 (define (get-macro name)
   (eval (get name 'sex-macro)))
 
-(define (sex-macro? form)
+(define (macro? form)
   (and (list? form)
        (symbol? (car form))
        (get (car form) 'sex-macro)))
 
 (define (apply-macro form)
-  (assert (sex-macro? form)
+  (assert (macro? form)
           (fmt #f (car form) " is not a macro"))
   (apply (get-macro (car form))
          (cdr form)))