Add Swift Package Manager support about ampere

[ole]

See Daniel Duan's article about automating testing for all permutations of CocoaPods/Carthage/SwiftPM and macOS/iOS/tvOS/watchOS: http://dduan.net/2016/10/10/distribution-tests/

[ole]

SwiftPM currently hardcodes the macOS deployment target to 10.10 (Ampere needs 10.12). Here is a workaround, but it's not in 3.0. apple/swift-package-manager#715

[billabt]

What version of the Swift toolchain has the fix for this problem in it?

Using swift-3.0.1-RELEASE, I see the default target overriding my specified target...

other-args: ["-j8","-D","SWIFT_PACKAGE","-Onone","-g","-enable-testing","-F","/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/Library/Frameworks","-target","x86_64-apple-macosx10.12","-target","x86_64-apple-macosx10.10","-sdk","/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk","-Xcc","-fmodule-map-file=/Users/babt/Source/IBMSwift/Open Source/BlueRSA/Packages/CommonCrypto-0.1.4/module.modulemap","-module-cache-path","/Users/babt/Source/IBMSwift/Open Source/BlueRSA/.build/debug/ModuleCache"]

[ole]

$ cd swift-source
$ swift/utils/update-checkout
$ cd swiftpm
$ git branch -r --contains 28e221b
  origin/HEAD -> origin/master
  origin/master
  origin/master-next
  origin/swift-3.1-branch

So it seems this will be part of Swift 3.1.

[ole]

See #9 for a version that builds with the Swift Package Manager (using a recent Swift snapshot).

[ole]

Taking this issue up again now that Xcode 11 has SwiftPM support. My plan is to fully migrate to SwiftPM and delete the Xcode project.

Checklist:

• Add Package manifest
• Change directory structure to accomodate SwiftPM
• Delete Xcode project
• Set macOS and iOS deployment targets
• Add Docker config for testing under Linux
• Update .gitignore
• Update usage instructions in readme
• Update .travis.yml to use Docker or use GitHub Actions