use tcell via porting over code from awesome-gocui

vendor/github.com/gdamore/encoding/utf8.go

@@ -0,0 +1,35 @@
+// Copyright 2015 Garrett D'Amore
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use file except in compliance with the License.
+// You may obtain a copy of the license at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package encoding
+
+import (
+	"golang.org/x/text/encoding"
+)
+
+type validUtf8 struct{}
+
+// UTF8 is an encoding for UTF-8.  All it does is verify that the UTF-8
+// in is valid.  The main reason for its existence is that it will detect
+// and report ErrSrcShort or ErrDstShort, whereas the Nop encoding just
+// passes every byte, blithely.
+var UTF8 encoding.Encoding = validUtf8{}
+
+func (validUtf8) NewDecoder() *encoding.Decoder {
+	return &encoding.Decoder{Transformer: encoding.UTF8Validator}
+}
+
+func (validUtf8) NewEncoder() *encoding.Encoder {
+	return &encoding.Encoder{Transformer: encoding.UTF8Validator}
+}