split semantic processing and fmt-c code generation

Introducing Sex SEMantic ENgine: the semen.
Also split reader to other file (it can be replaced in the future).
Macro expansion inside Sex code doesn't work yet, and it must be done
in semen, not during fmt-c generation as before.

tests/semen.scm

@@ -0,0 +1,34 @@
+(define print-str-fn
+  '(fn void print-str ((string s))
+       (printf "%s" s)))
+
+(define sum-fn
+  '(pub fn float sum ((int a) (int b))
+        (return (cast float (+ a b)))))
+
+(test-begin "semen")
+(test-assert (sex-fn? print-str-fn))
+(test #f (sex-fn-public? print-str-fn))
+(test 'void (sex-fn-return-type print-str-fn))
+(test 'print-str (sex-fn-name print-str-fn))
+(test '((string s)) (sex-fn-arglist print-str-fn))
+(test '(fn void print-str ((string s))) (sex-fn-prototype print-str-fn))
+(test '((printf "%s" s)) (sex-fn-body print-str-fn))
+
+(test-assert (sex-fn? sum-fn))
+(test #t (sex-fn-public? sum-fn))
+(test 'float (sex-fn-return-type sum-fn))
+(test 'sum (sex-fn-name sum-fn))
+(test '((int a) (int b)) (sex-fn-arglist sum-fn))
+(test '(pub fn float sum ((int a) (int b))) (sex-fn-prototype sum-fn))
+(test '((return (cast float (+ a b)))) (sex-fn-body sum-fn))
+
+(define sex-code
+  '((defmacro (sum-var name a b c)
+      `(var ,name ,(+ a b c)))
+
+    (sum-var v 1 2 3)))
+
+(test '((var v 6)) (semen-process sex-code))
+
+(test-end)