Fix text encoder/decoder of CtdEditor.

[kenjiuno]

Added encoding selector.

Implement Japanese encoder/decoder.

The international encoder/decoder will work even if used for Japanese data.

Remove JapaneseCtdEncoder which is not implemented yet.

Rename InternationalCtdEncoder into UnifiedCtdEncoder.

The refined decoder interface:

    public interface ICtdMessageDecode
    {
        string ToText(byte[] data, CtdToTextOptions opts = null);
    }

    public class CtdToTextOptions
    {
        /// <summary>
        /// Allow to decode unknown as `{:unk FF}` alternative instead of throwing an exception.
        /// </summary>
        public bool AllowUnkUsage { get; set; } = true;

        /// <summary>
        /// Decode input as Shift_JIS encoding.
        /// </summary>
        public bool DecodeAsShiftJIS { get; set; }
    }

The refined encoder interface:

    public interface ICtdMessageEncode
    {
        byte[] FromText(string text, CtdFromTextOptions opts = null);
    }

    public class CtdFromTextOptions
    {
        /// <summary>
        /// Encode input as Shift_JIS encoding.
        /// </summary>
        public bool EncodeAsShiftJIS { get; set; }
    }

Apply DI partially.