Support MacOS for Carthage Dependencies

[keefertaylor]

Building this library for MacOS with Carthage previously resulted in an error (see #4).

I performed the following steps to upgrade the .xcodeproj for MacOS compatibility with Carthage:

• Open xcodeproj, run all update scripts recommended by XCode (swift 5 migration, etc)
• Set supportedPlatforms to macosx, iphoneos, iphonesimulator in build configuration
• Replace #import <UIKit/UIKit.h> with #import <Foundation/Foundation.h>. UIKit imports Foundation, but the source files do not use any UIKit based classes and UIKit is not available on MacOS.

To test, I verified that my Carthage based project can now build this library on both iOS and OSX (example PR with continuous CI: keefertaylor/TezosKit#153).

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Fixes #4

[koraykoska]

Please make sure Travis completes successfully

[koraykoska]

Done?

[keefertaylor]

Apologies that this is stale. I'll poke at this today and see if I can get it working.

[keefertaylor]

It isn't immediately clear to me why this is failing.

There's a couple variables here:

• You're using a pretty old 2+ years image of XCode (9.2 vs the current 11.3)
• Your dependencies are out of date (so I can't easily upgrade to a modern version of xcode)
• After upgrading, I get missing rpath@ errors, for reasons I can't discern

Without updating, I can't get this to build locally and reproduce the failures we see on CI. I do believe this PR works though (and I am actually consuming this PR in a production project from my fork), it's just that the testbed project isn't passing.

I opened #9 to address changes to the build system. I'm confident if we can get that to a passing state then we should be able to make this PR pass CI quite easily.

[keefertaylor]

Update: I actually believe this project is broken at head, see #10.

I no longer believe that build breaks are related to this PR.

[koraykoska]

@keefertaylor Can you see the actual error message? I will try to fix this at head so we can apply it here.