Marker zoom scaling does not work well in an AC map

[alan-wu]

The changes on marker zoom scaling (8602626) does not work well in AC map.

I am keen to stick with a fix size value on AC maps and provide an option to override that.

[napakalas]

Pretty sure this is the same problem reported at #76

[alan-wu]

Pretty sure this is the same problem reported at #76

@napakalas The changes in the commit is specifically targeting the markers but similar changes may have taken place around the same time.