detectRetina not implemented?

[lachlanphillips]

maptalks's version and what browser you use? Latest. Chrome.

Issue description It looks like detectRetina might not yet be implemented in maptalks. This is a common feature in comparable map tools. The end result is that on retina displays, the 3D is sharp, but the tiles are low res. I believe it's a simple enough thing to implement - it's just about getting the higher resolution tiles - but unfortunately it's beyond me to contribute.

Cheers