allow pybullet to connect to GRPC server. (need to use flag --enable_grpc in premake build system)

add grpcPlugin, it can work in GUI, SHARED_MEMORY_SERVER, DIRECT and other modes.
example script to start server from pybullet:
import pybullet as p
p.connect(p.GUI)
#if statically linked plugin
id = p.loadPlugin("grpcPlugin")
#dynamics loading the plugin
#id = p.loadPlugin("E:/develop/bullet3/bin/pybullet_grpcPlugin_vs2010_x64_debug.dll", postFix="_grpcPlugin")

#start the GRPC server at hostname, port
if (id>=0):
	p.executePluginCommand(id, "localhost:1234")

Only in DIRECT mode, since there is no 'ping' you need to call to handle RCPs:
numRPC = 10
while (1):
	p.executePluginCommand(id, intArgs=[numRPC])

examples/SharedMemory/plugins/grpcPlugin/grpcPlugin.h

@@ -0,0 +1,29 @@
+#ifndef GRPC_PLUGIN_H
+#define GRPC_PLUGIN_H
+
+#include "../b3PluginAPI.h"
+
+#ifdef __cplusplus
+extern "C" 
+{
+#endif
+
+//the following 3 APIs are required
+B3_SHARED_API int initPlugin_grpcPlugin(struct b3PluginContext* context);
+B3_SHARED_API void exitPlugin_grpcPlugin(struct b3PluginContext* context);
+B3_SHARED_API int executePluginCommand_grpcPlugin(struct b3PluginContext* context, const struct b3PluginArguments* arguments);
+
+//all the APIs below are optional
+B3_SHARED_API int preTickPluginCallback_grpcPlugin(struct b3PluginContext* context);
+B3_SHARED_API int postTickPluginCallback_grpcPlugin(struct b3PluginContext* context);
+
+B3_SHARED_API int processClientCommands_grpcPlugin(struct b3PluginContext* context);
+
+
+
+
+#ifdef __cplusplus
+};
+#endif
+
+#endif//#define GRPC_PLUGIN_H