- Let Xcode 8 update settings on the projects/schemes.
- Migrate Swift tests to Swift 3 syntax.
- Update the build/test script:
  - Require Xcode 8 (because of the Swift 3 requirement for tests)
  - Update the devices to what Xcode 8 has (8.x simulator seem to fail even
    though they can be downloaded in Xcode 8)
- Update the travis images to ones with Xcode 8.

Add the `nullable` qualifier to return types of Objective-C methods that
can return a nil due to errors. This change makes these methods
compatible with the Swift 2 try-catch syntax.

Note: Breaking API change on the Dictionary classes.

The numeric value classes were using "Value" in the naming, but this silently
collided with the KVC category on NSObject; meaning KVC code could break up a
keypath and call these selectors with the wrong types leading to crashes (even
though the code all would compile cleanly).

- Rename the methods to use the "type" instead of literal "Value".
- Update all the impls and tests.
- Enable the warning that will catch issues like this in the future.

Fixes https://github.com/google/protobuf/issues/1616

- Let Xcode update the projects, schemes, and info.plists.
- Add workaround for shallow analyzer issues in current Xcode versions (deep analyze gets things correct).
- Tweak the Swift based tests to avoid warnings from Xcode 7's XCTest using optionals for autoenclosure results.
- No longer tag the ObjC iOS travis test as flaky, xctool seems to manage the simulator pretty well.

Add the clang annotations to the objc library and generated code to help with Swift bridging and compiler checks.

- Style fixups in the code.
- map<> serialization fixes and more tests.
- Autocreation of map<> fields (to match repeated fields).
- @@protoc_insertion_point(global_scope|imports).
- Fixup proto2 syntax extension support.
- Move all startup code to +initialize so it happen on class usage and not app startup.
- Have generated headers use forward declarations and move imports into generated code, reduces what is need at compile time to speed up compiled and avoid pointless rippling of rebuilds.