beautifying engine API 1

Signed-off-by: Wayne Wolf <wayne.ron.wu@googlemail>
beautifying engine API 2

Signed-off-by: Wayne Wolf <wayne.ron.wu@googlemail>
beautifying engine API 3

Signed-off-by: Wayne Wolf <wayne.ron.wu@googlemail>
beautifying engine API 4

Signed-off-by: Wayne Wolf <wayne.ron.wu@googlemail>
beautifying engine API 5

also make Node weak refernece program to make sure program destroctor
called when egl context available

Signed-off-by: Wayne Wolf <wayne.ron.wu@googlemail>
fix possible virtual dtor memory leak

Signed-off-by: Wayne Wolf <wayne.ron.wu@googlemail>
fix some warnings

Signed-off-by: Wayne Wolf <wayne.ron.wu@googlemail>
add update interface in before drawing each frame

Signed-off-by: Wayne Wolf <wayne.ron.wu@googlemail>