Update for Swift 3

[boundsj]

This ports the Swift 2.2 implementation to Swift 3. It is a work in progress and there are several known issues but it is functional and can be used, for now, to help test applications written with the Xcode 8 and Swift 3 betas that use MapboxStatic.

Todo:

• [x] Syntax update to Swift 3 in library, example apps, and playgrounds
• [ ] Use Swift 3 version of OHHTTPStubs
• [ ] Consider wrapping changes in #if swift(>=3.0) blocks to help maintain backwards compatibility with Swift 2.2+

  Known issues:

• Tests won't run because the HTTP mock library is not updated, yet
• The most obvious port of allowedCharacterSet in Overlay.swift seems to cause an exception in the first Xcode 8 beta. This needs more investigation. For now, the workaround is to use an inverted CharacterSet for MBCustomMarker and CharacterSet.urlPathAllowed for GeoJSON and Path overlays.

[1ec5]

The most obvious port of allowedCharacterSet in Overlay.swift seems to cause an exception in the first Xcode 8 beta.

https://openradar.appspot.com/26880260

[1ec5]

Superseded by #41.

[1ec5]

The saga continues in #50.