various improvements from MapBox 0.5.0 release
o Refactored contraints so that tilesource constraints are always intersected with user supplied constraints
o Merge fix
o Removed unnecessary RMRequireAsset calls in [RMMapView setShowsUserLocation:]
o Licence and copyright updates
o Changed [RMMapView resourceImageNamed:] so that we don't need an image bundle in this fork
o Sample code updates
o Project update
o Prevent double tile downloads
o Some code improvements (NS_ENUM, instancetype)
o Better synchronization for annotations in the quad tree
Merge branch 'release' into develop
o Implementation of the UTM coordinate grid in RMCoordinateGridSource
Merge branch 'develop' into release