add make.bat for windows (#1272)

* add make.bat for windows

* fix syntax

* fix commented part

* fix description

protobuf-definitions/make_for_win.bat

+rem variables
+
+rem GRPC-TOOLS required. Install with `nuget install Grpc.Tools`. 
+rem Then un-comment and replace [DIRECTORY] with location of files.
+rem For example, on Windows, you might have something like:
+rem set COMPILER=Grpc.Tools.1.14.1/tools/windows_x64
+
+set SRC_DIR=proto\mlagents\envs\communicator_objects
+set DST_DIR_C=..\UnitySDK\Assets\ML-Agents\Scripts\CommunicatorObjects
+set DST_DIR_P=..\ml-agents
+set PROTO_PATH=proto
+
+set PYTHON_PACKAGE=mlagents\envs\communicator_objects
+
+rem clean
+rd /s /q %DST_DIR_C%
+rd /s /q %DST_DIR_P%\%PYTHON_PACKAGE%
+mkdir %DST_DIR_C%
+mkdir %DST_DIR_P%\%PYTHON_PACKAGE%
+
+rem generate proto objects in python and C#
+
+for %%i in (%SRC_DIR%\*.proto) do (
+    protoc --proto_path=proto --csharp_out=%DST_DIR_C% %%i
+    protoc --proto_path=proto --python_out=%DST_DIR_P% %%i
+)
+
+rem grpc
+
+set GRPC=unity_to_external.proto
+
+%COMPILER%\protoc --proto_path=proto --csharp_out %DST_DIR_C% --grpc_out %DST_DIR_C% %SRC_DIR%\%GRPC% --plugin=protoc-gen-grpc=%COMPILER%\grpc_csharp_plugin.exe
+python3 -m grpc_tools.protoc --proto_path=proto --python_out=%DST_DIR_P% --grpc_python_out=%DST_DIR_P% %SRC_DIR%\%GRPC%
+
+rem Generate the init file for the python module
+rem rm -f $DST_DIR_P/$PYTHON_PACKAGE/__init__.py
+setlocal enabledelayedexpansion
+for %%i in (%DST_DIR_P%\%PYTHON_PACKAGE%\*.py) do ( 
+set FILE=%%~ni
+rem echo from .$(basename $FILE) import * >> $DST_DIR_P/$PYTHON_PACKAGE/__init__.py
+echo from .!FILE! import * >> %DST_DIR_P%\%PYTHON_PACKAGE%\__init__.py
+)
+