Adding support for files as UTF-8 and Shift-JSI/SJIS encoding

[azerios]

Using files having UTF-8 and Shift-JSI/SJIS encoding it's possible to extract Japanese words which are inside.

Fixing #56

Usage example

// Enable encoding detection for Japanese text files
var options = new FilterReaderOptions 
{ 
    UseEncodingDetection = true 
};

// Read UTF-8 encoded Japanese file
using (var reader = new FilterReader("japanese_utf8.txt", filterReaderOptions: options))
{
    var content = reader.ReadToEnd();
    Console.WriteLine(content); // Correctly displays: テスト
}

// Read Shift-JIS encoded Japanese file
using (var reader = new FilterReader("japanese_shiftjis.txt", filterReaderOptions: options))
{
    var content = reader.ReadToEnd();
    Console.WriteLine(content); // Correctly displays: テスト
}

// Search for Japanese text in log files
var searchReader = new IFilterTextViewer.Reader(options);
bool found = searchReader.FileContainsText("app.log", "エラー", ignoreCase: true);