Implement configurable detach key

Implement configurable detach keys (for `attach`, exec`, `run` and
`start`) using the client-side configuration

- Adds a `--detach-keys` flag to `attach`, `exec`, `run` and `start`
  commands.
- Adds a new configuration field (in `~/.docker/config.json`) to
  configure the default escape keys for docker client.

Signed-off-by: Vincent Demeester <vincent@sbr.pm>

term/ascii_test.go

@@ -0,0 +1,43 @@
+package term
+
+import "testing"
+
+func TestToBytes(t *testing.T) {
+	codes, err := ToBytes("ctrl-a,a")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(codes) != 2 {
+		t.Fatalf("Expected 2 codes, got %d", len(codes))
+	}
+	if codes[0] != 1 || codes[1] != 97 {
+		t.Fatalf("Expected '1' '97', got '%d' '%d'", codes[0], codes[1])
+	}
+
+	codes, err = ToBytes("shift-z")
+	if err == nil {
+		t.Fatalf("Expected error, got none")
+	}
+
+	codes, err = ToBytes("ctrl-@,ctrl-[,~,ctrl-o")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(codes) != 4 {
+		t.Fatalf("Expected 4 codes, got %d", len(codes))
+	}
+	if codes[0] != 0 || codes[1] != 27 || codes[2] != 126 || codes[3] != 15 {
+		t.Fatalf("Expected '0' '27' '126', '15', got '%d' '%d' '%d' '%d'", codes[0], codes[1], codes[2], codes[3])
+	}
+
+	codes, err = ToBytes("DEL,+")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(codes) != 2 {
+		t.Fatalf("Expected 2 codes, got %d", len(codes))
+	}
+	if codes[0] != 127 || codes[1] != 43 {
+		t.Fatalf("Expected '127 '43'', got '%d' '%d'", codes[0], codes[1])
+	}
+}