Add tvOS target and fix Carthage errors

[nickygerritsen]

This is a preliminary pull request to add a tvOS target.

First of all it fixes strange carthage errors when building the watchOS target (see Carthage/Carthage#784)

Furthermore it thus adds the tvOS targets, but I have unshared the schemes for now. This is for two reasons:

• The CommonCrypto scheme needs XCode-beta.app for the correct header files
• Otherwise it fail when using Carthage in XCode 7.0

You can either wait before merging this in until tvOS is publicly available (I will then update this PR to not link to the beta and share the schemes), or merge it in now and create a branch that does enable the schemes.
Doing the latter allows people to already use the tvOS version using your repo. If you decide not to do that yet, people can use my branch at https://github.com/nickygerritsen/Crypto/tree/add-tvos-target for that.

This PR is also there so that other people know that they do not need to also create a tvOS PR.

[nickygerritsen]

OK I redid this PR so it now also includes the Zlib thingy and it also now uses the non-beta XCode paths.

For me it is now done, so @soffes can take a look at it and maybe merge it :)

[nickygerritsen]

btw it seems Carthage/Carthage#784 is back again now, but lets first merge this and afterwards perhaps recreate the targets again to fix the issue

[soffes]

Thanks!