use new edown_make script to generate documentation

To eliminate the rebar dependency on edown, change the "make edoc"
target to use the new edown_make script to generate documentation.

Makefile

@@ -6,13 +6,18 @@ DEST:=$(PREFIX)$(PROJECT)
 # from https://github.com/basho/rebar .
 REBAR=rebar
 
+# Expect to find edown_make in the PATH. This is needed only to generate
+# documentation. If you don't have it, you can get it from
+# https://github.com/esl/edown.git .
+EDOWN_MAKE=edown_make
+
 .PHONY: all edoc test clean build_plt dialyzer
 
 all:
 	@$(REBAR) get-deps compile
 
 edoc:
-	@$(REBAR) doc
+	$(EDOWN_MAKE) -config edown.config
 
 test:
 	@rm -rf .eunit

edown.config

@@ -0,0 +1,11 @@
+%% -*- erlang -*-
+{erlsha2, ".", [{doclet, edown_doclet},
+               {pretty_printer, erl_pp},
+               {src_path, ["src/"]},
+               {subpackages, true},
+               {stylesheet, ""},
+               {image, ""},
+               {app_default,"http://www.erlang.org/doc/man"},
+               {top_level_readme,
+                {"./doc/README.md",
+                 "http://github.com/vinoski/erlsha2"}}]}.

rebar.config

@@ -1,3 +1,4 @@
+%% -*- erlang -*-
 {so_name, "erlsha2_nif.so"}.
 
 {port_envs, [{"DRV_CFLAGS", "$DRV_CFLAGS -O3 -I."},
@@ -9,10 +10,7 @@
 {pre_hooks, [{compile, "c_src/config.sh c_src/config.h"},
              {clean, "rm -f c_src/config.h"}]}.
 
-%% The following two terms are required only for generating documentation,
-%% and so are commented out by default.
-%%{deps, [{edown, ".*", {git, "git://github.com/esl/edown.git", "HEAD"}}]}.
-%%{edoc_opts, [{doclet, edown_doclet},
-%%             {pretty_printer, erl_pp},
-%%             {src_path, ["src/"]},
-%%             {subpackages, true}]}.
+{edoc_opts, [{doclet, edown_doclet},
+             {pretty_printer, erl_pp},
+             {src_path, ["src/"]},
+             {subpackages, true}]}.