improvements from MapBox for 1.0.0 to latest

These are our latest improvements leading up to our 1.0.0 release back in the Spring and everything since then. Somewhat significant API changes, particularly ARC, but updating projects is pretty straightforward. As always, feel free to post any questions and we can go over things in detail. 

 * Automatic Reference Counting (ARC) support. (#78)
 * Dropped iOS 4 support. 
 * Allow for library-wide custom `User-Agent` header for all network requests. (mapbox/mapbox-ios-sdk#22)
 * Updated [SMCalloutView](https://github.com/nfarina/calloutview). 
 * Improvements to annotation selection. (mapbox/mapbox-ios-sdk#189)
 * Allow selection of `nil` annotation to deselect. 
 * Updated project for Xcode 4.6. 
 * Various documentation improvements. 
 * Fail map view `init` when passed an invalid tile source. 
 * Renamed long-press map gesture for consistency with Apple. 
 * Added long-press annotation gesture. (mapbox/mapbox-ios-sdk#181)
 * Renamed some properties to be more intuitive to use and easier to autocomplete (`draggingEnabled`, `bouncingEnabled`, `clusteringEnabled`). 
 * Don't change map center if value passed isn't different. (mapbox/mapbox-ios-sdk#186)
 * Silence some iOS 6 deprecations since iOS 5 is still supported. (mapbox/mapbox-ios-sdk#179)
 * Adjust user heading path width based on accuracy. (mapbox/mapbox-ios-sdk#75)
 * Annotation layers shouldn't be draggable by default. 
 * Clustering improvements to make API simpler (`isClusterAnnotation`, `clusteredAnnotations`). 
 * Don't begin tap gesture zooms in/out if already at max/min zoom. (mapbox/mapbox-ios-sdk#186)
 * Annotation layer hit test cleanups. (mapbox/mapbox-ios-sdk#171)
 * Properly notify map delegate of callout auto-moves ending. 
 * No longer allow callouts on cluster annotations. (mapbox/mapbox-ios-sdk#171)
 * Cleaner API for move/zoom delegate notification commits. 
 * Properly sort circles with other shapes in z-ordering. 
 * Removed slight delay when displaying callouts. 
 * Fix shape/circle hit detection passed on presence of fill color. 
 * Public/private header cleanup. The idea here is to make private any headers that a normal user of the library would not use, such as `RMMapTiledLayerView.h`. 
 * Added `fillPatternImage` to `RMShape` and `RMCircle`. 
 * Projected point equality test bug fix. 
 * User location accuracy circle now bounces on first location update. (mapbox/mapbox-ios-sdk#27)
 * Removed `boundingMask` & made `minZoom` automatic per passed `frame`. (mapbox/mapbox-ios-sdk#12)
 * Readjust loading tile background after map frame changes. (mapbox/mapbox-ios-sdk#156)