add MKMapView extension to calculate zoom level
Merge branch 'master' of https://github.com/wesleysui/MarketManager

Conflicts:
	MarketManager/Base.lproj/Main.storyboard
Merge branch 'master' of https://github.com/wesleysui/MarketManager

Conflicts:
	MarketManager/Base.lproj/Main.storyboard
Merge branch 'master' of https://github.com/wesleysui/MarketManager