Made it possible to use (refresh-makefile) in order to refresh an edited makefile on the fly.

scrbl/racket-makefile.scrbl

@@ -3,7 +3,7 @@
 @(require (for-label racket/base
                      racket/file
                      (only-in racket-makefile
-                              target deps phony default-target make
+                              target deps phony default-target make refresh-makefile
                               run raco rm-f rm-rf cleanup
                               list-dir/files list-files list-dirs
                               $target $deps $<)))
@@ -31,7 +31,7 @@ raco pkg install
 For a versioned archive, specify the package name explicitly:
 
 @verbatim{
-raco pkg install --name racket-makefile racket-makefile-0.1.6.zip
+raco pkg install --name racket-makefile racket-makefile-0.1.8.zip
 }
 
 After installation a makefile can start with:
@@ -109,6 +109,22 @@ the targets. Then execute targets in the Interactions window:
 > (make clean all)
 }
 
+After editing the makefile, reload its target definitions in the same Racket
+process with:
+
+@verbatim{
+> (refresh-makefile)
+> (make all)
+}
+
+@defproc[(refresh-makefile) void?]{
+Reloads the most recently loaded @tt{racket-makefile} source file and registers
+its targets again without restarting the Racket process. This works for both
+@tt{#lang racket-makefile} and ordinary @tt{#lang racket} makefiles that require
+@tt{main.rkt}. Modules required by the makefile that are already instantiated
+are reused. This is useful for makefiles that require expensive libraries.
+}
+
 @section{Targets and dependencies}
 
 @defform[(target name (deps dependency ...) body ...)]{