Commit the generated manpage.mld

Allows to build the documentation on <4.10, as the generating program
can't run on these versions.
Useful feedback when modifying the CLI.
Reduce the complexity of the Dune rules for building the doc. Might
allow the reference driver to build it, for example.

Author: Julow

doc/dune

@@ -1,11 +1,18 @@
 (rule
  (action
   (with-stdout-to
-   manpage.mld
+   manpage.gen.mld
    (pipe-stdout
     (run odoc)
     (run gen_manpage/gen_manpage.exe)))))
 
+(rule
+ (alias runtest)
+ (enabled_if
+  (> %{ocaml_version} 4.10))
+ (action
+  (diff manpage.mld manpage.gen.mld)))
+
 (documentation
  (package odoc)
  (mld_files