Annotate generated escript with last release

End result should allow to look like this:

    $ head -n 3 rebar3
    #!/usr/bin/env escript
    %% Rebar3 3.14.0-rc1
    %%! +sbtu +A1

This will allow tools like mix to read the top of the file to know the
version being used in the current path (when using features that aren't
forwards-compatible) without having to invoke the tool itself.

The version (full dynamic one) is also added to the local install:

    $ head -n 2 /home/ferd/.cache/rebar3/bin/rebar3
    #!/usr/bin/env sh
    ## Rebar3 3.14.0-rc1+build.4599.ref6b0f90d

The `##` comments are used to keep a fixed width over the other form.

To be backported to 3.13.2 as well.

rebar.config

@@ -24,6 +24,7 @@
              ]}.
 
 {escript_name, rebar3}.
+{escript_comment, "%%Rebar3 3.14.0-rc1\n"}.
 {escript_emu_args, "%%! +sbtu +A1\n"}.
 %% escript_incl_extra is for internal rebar-private use only.
 %% Do not use outside rebar. Config interface is not stable.

src/rebar_prv_local_install.erl

@@ -62,8 +62,9 @@ format_error(Reason) ->
     io_lib:format("~p", [Reason]).
 
 bin_contents(OutputDir) ->
+    {ok, Vsn} = application:get_key(rebar, vsn),
     <<"#!/usr/bin/env sh
-
+## Rebar3 ", (iolist_to_binary(Vsn))/binary, "
 erl -pz ", (rebar_utils:to_binary(OutputDir))/binary,"/*/ebin +sbtu +A1 -noshell -boot start_clean -s rebar3 main $REBAR3_ERL_ARGS -extra \"$@\"
 ">>.