Support for tvOS

This release brings breaking changes and should be only when building with at least Xcode 7.1.

Changes

• Support for new platform tvOS
• Explicitly enable bitcode via ENABLE_BITCODE for all platforms but macosx to maximize compatibility of built frameworks
• Fixes VALID_ARCHS for simulator platforms. (xcodebuild itself doesn't seem to care though and builds only relevant architectures anyway, even if they are not included. But at least the values match with what can be effectively built. That might be relevant for secondary tooling.)

Credits

Thanks to @brentleyjones and @flovilmart for their contributions.