Support for Golang GRPC (Experimental) (#4082)

* support for grpc golang

* refactored grpc go generator

* added grpc-go test and refactored

* refactored idl_gen_grpc.cpp

* fixed grpc generate method name

* refactored flatc and fixed line length issue

* added codec to go lib and fixed formatting issues

* fixed spacing issues

tests/MyGame/Example/MonsterStorage_grpc.go

@@ -0,0 +1,106 @@
+//Generated by gRPC Go plugin
+//If you make any local changes, they will be lost
+//source: monster_test
+
+package Example
+
+import "github.com/google/flatbuffers/go"
+
+import (
+  context "golang.org/x/net/context"
+  grpc "google.golang.org/grpc"
+)
+
+// Client API for MonsterStorage service
+type MonsterStorageClient interface{
+  Store(ctx context.Context, in *flatbuffers.Builder, 
+  	opts... grpc.CallOption) (* Stat, error)  
+  Retrieve(ctx context.Context, in *flatbuffers.Builder, 
+  	opts... grpc.CallOption) (* Monster, error)  
+}
+
+type monsterStorageClient struct {
+  cc *grpc.ClientConn
+}
+
+func NewMonsterStorageClient(cc *grpc.ClientConn) MonsterStorageClient {
+  return &monsterStorageClient{cc}
+}
+
+func (c *monsterStorageClient) Store(ctx context.Context, in *flatbuffers.Builder, 
+	opts... grpc.CallOption) (* Stat, error) {
+  out := new(Stat)
+  err := grpc.Invoke(ctx, "/Example.MonsterStorage/Store", in, out, c.cc, opts...)
+  if err != nil { return nil, err }
+  return out, nil
+}
+
+func (c *monsterStorageClient) Retrieve(ctx context.Context, in *flatbuffers.Builder, 
+	opts... grpc.CallOption) (* Monster, error) {
+  out := new(Monster)
+  err := grpc.Invoke(ctx, "/Example.MonsterStorage/Retrieve", in, out, c.cc, opts...)
+  if err != nil { return nil, err }
+  return out, nil
+}
+
+// Server API for MonsterStorage service
+type MonsterStorageServer interface {
+  Store(context.Context, *Monster) (*flatbuffers.Builder, error)  
+  Retrieve(context.Context, *Stat) (*flatbuffers.Builder, error)  
+}
+
+func RegisterMonsterStorageServer(s *grpc.Server, srv MonsterStorageServer) {
+  s.RegisterService(&_MonsterStorage_serviceDesc, srv)
+}
+
+func _MonsterStorage_Store_Handler(srv interface{}, ctx context.Context,
+	dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
+  in := new(Monster)
+  if err := dec(in); err != nil { return nil, err }
+  if interceptor == nil { return srv.(MonsterStorageServer).Store(ctx, in) }
+  info := &grpc.UnaryServerInfo{
+    Server: srv,
+    FullMethod: "/Example.MonsterStorage/Store",
+  }
+  
+  handler := func(ctx context.Context, req interface{}) (interface{}, error) {
+    return srv.(MonsterStorageServer).Store(ctx, req.(* Monster))
+  }
+  return interceptor(ctx, in, info, handler)
+}
+
+
+func _MonsterStorage_Retrieve_Handler(srv interface{}, ctx context.Context,
+	dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
+  in := new(Stat)
+  if err := dec(in); err != nil { return nil, err }
+  if interceptor == nil { return srv.(MonsterStorageServer).Retrieve(ctx, in) }
+  info := &grpc.UnaryServerInfo{
+    Server: srv,
+    FullMethod: "/Example.MonsterStorage/Retrieve",
+  }
+  
+  handler := func(ctx context.Context, req interface{}) (interface{}, error) {
+    return srv.(MonsterStorageServer).Retrieve(ctx, req.(* Stat))
+  }
+  return interceptor(ctx, in, info, handler)
+}
+
+
+var _MonsterStorage_serviceDesc = grpc.ServiceDesc{
+  ServiceName: "Example.MonsterStorage",
+  HandlerType: (*MonsterStorageServer)(nil),
+  Methods: []grpc.MethodDesc{
+    {
+      MethodName: "Store",
+      Handler: _MonsterStorage_Store_Handler, 
+    },
+    {
+      MethodName: "Retrieve",
+      Handler: _MonsterStorage_Retrieve_Handler, 
+    },
+  },
+  Streams: []grpc.StreamDesc{
+  },
+}
+