support printing version and help

Author: tony612

lib/protobuf/protoc/cli.ex

@@ -1,4 +1,28 @@
 defmodule Protobuf.Protoc.CLI do
+  @moduledoc false
+
+  def main(["--version"]) do
+    {:ok, version} = :application.get_key(:protobuf, :vsn)
+    IO.puts to_string(version)
+  end
+
+  def main([opt]) when opt in ["--help", "-h"] do
+    IO.puts """
+    protoc plugin for generating Elixir code
+
+    See `protoc -h` and protobuf-elixir for details.
+    NOTICE: protoc-gen-elixir(this name is important) must be in $PATH
+
+    Examples:
+      $ protoc --elixir_out=./lib your.proto
+      $ protoc --elixir_out=plugins=grpc:./lib/ *.proto
+      $ protoc -I protos --elixir_out=./lib protos/namespace/*.proto
+
+    Options:
+    --version       Print version of protobuf-elixir
+    """
+  end
+
   def main(_) do
     # https://groups.google.com/forum/#!topic/elixir-lang-talk/T5enez_BBTI
     :io.setopts(:standard_io, encoding: :latin1)

mix.exs

@@ -1,7 +1,7 @@
 defmodule Protobuf.Mixfile do
   use Mix.Project
 
-  @version "0.7.0"
+  @version "0.7.1"
 
   def project do
     [
@@ -29,7 +29,7 @@ defmodule Protobuf.Mixfile do
   end
 
   defp escript do
-    [main_module: Protobuf.Protoc.CLI, name: "protoc-gen-elixir", app: nil]
+    [main_module: Protobuf.Protoc.CLI, name: "protoc-gen-elixir"]
   end
 
   defp description do