Add tvOS support

[dimazen]

Adding tvOS support with Xcode 8.3

[dimazen]

Not sure what exactly goes wrong, but it says that

Tests/Support/objc-build-scripts/cibuild: line 110:  1360 Abort trap: 6           xctool -project "$XCODEPROJ" $XCTOOL_OPTIONS "$@" 2>&1
ERROR: Unexpected action: test

I'm also not sure why to use Rakefile while we can go with .travis.yml similar to what Alamofire has.

[orta]

Last time this was attempted it got stopped at some weird code signing issues - #175

I think switching to a similar .travis.yml as Alamofire may be simpler than the Rakefile approach WRT testing too.

[dimazen]

@orta Sorry, it took me longer than I would expect :)
So far I've added tvOS framework as well as setup unit tests execution for all of the supported targets in Debug + Release.

The only thing I'm not quite sure about is whether I need to add libExpecta-tvOS and do we need to run tests for iOS 8 and 9? I've skipped tests for iOS 8 / 9 due to the Travis CI issue travis-ci/travis-ci#7638.

Also do I have to remove rakefile and objc-build-scripts?

[orta]

Never worry about your time WRT shipping OSS. Doesn't look like anyone is being blocked by your work.

I think as long as there is the ability to generate a library that can be consumed by others (@tonyarnold has been shipping those with releases) then I think that's really the only responsibility left in the Rakefile or the build scripts.

[dimazen]

I ran (according to the Carthage guide)

carthage build --no-current-skip
carthage archive 

and got the following output (similar to what Tony Arnold did)
Expecta.framework.zip