use tcell via porting over code from awesome-gocui

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

@@ -0,0 +1,36 @@
+// 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"
+)
+
+// ASCII represents the 7-bit US-ASCII scheme.  It decodes directly to
+// UTF-8 without change, as all ASCII values are legal UTF-8.
+// Unicode values less than 128 (i.e. 7 bits) map 1:1 with ASCII.
+// It encodes runes outside of that to 0x1A, the ASCII substitution character.
+var ASCII encoding.Encoding
+
+func init() {
+	amap := make(map[byte]rune)
+	for i := 128; i <= 255; i++ {
+		amap[byte(i)] = RuneError
+	}
+
+	cm := &Charmap{Map: amap}
+	cm.Init()
+	ASCII = cm
+}