Problem:    Compiler warning in direct write code.
Solution:   Add a type cast.

Problem:    Blank srceen when DirectWrite failed.
Solution:   Call redraw_later_clear() after recreating the Direct2D render
            target. (Ken Takata, closes #4172)

Problem:    DirectWrite doesn't take 'linespace' into account.
Solution:   Include 'linespace' in the position. (Ken Takata, closes #4137)

Problem:    MS-Windows: some text is not baseline aligned.
Solution:   Use bottom alignment. (Taro Muraoka, closes #4116, closes #1520)

Problem:    Slow redrawing with DirectX.
Solution:   Avoid calling gui_mch_flush() unnecessarily, especially when
            updating the cursor. (Ken Takata, closes #2560)

Problem:    DirectX scrolling can be slow, vertical positioning is off.
Solution:   Make scroll slightly faster when using "scrlines:1". Fix y
            position of displayed text. Fix DirectX with non-utf8 encoding.
            (Ken Takata, closes #2440)

Problem:    MS-Windows: drawing underline, curl and strike-throw is slow,
            mFallbackDC not properly updated.
Solution:   Several performance improvements. (Ken Takata, Taro Muraoka,
            Yasuhiro Matsumoto, closes #2401)

Problem:    MS-Windows: does not show colored emojis.
Solution:   Implement colored emojis. Improve drawing speed. Make 'taamode'
            work. (Taro Muraoka, Yasuhiro Matsumoto, Ken Takata, close #2375)

Problem:    Compiler warnings for non-virtual destructor.
Solution:   Mark the classe final. (Ken Takata)

Problem:    Compiler warning for non-virtual destructor.
Solution:   Make it virtual. (Yasuhiro Matsumoto)