Update README.md
Merge from https://github.com/avplayer/avplayer.git

Signed-off-by: Jack <jack.wgm@gmail.com>
change default to keep aspect

Signed-off-by: Jack <jack.wgm@gmail.com>
add gdi render implement

Signed-off-by: Jack <jack.wgm@gmail.com>
use to gdi render

Signed-off-by: Jack <jack.wgm@gmail.com>
Merge pull request #2 from Jackarain/master

gdi render improve