Implement and test explicate-control

.editorconfig

@@ -1,3 +1,4 @@
 [*.scm]
 indent_style = space
 indent_size = 2
+trim_trailing_whitespace = true

explicate-control.scm

@@ -27,6 +27,3 @@
   (match exp
      [`(let ([,v ,x]) ,b) (explicate-control-assign v x (explicate-control-assign var b c0-body))]
      [_ `(seq (assign ,var ,exp) ,c0-body)]))
-
-
-