Support swift package manager v4

[c-bata]

First, I need to say this changes are still not perfect because daltoniam/zlib-spm and daltoniam/Starscream didn't support Swift PM v4 yet. So I fork these and add changes to support it. You can check my changes via following pages.

• zlib-spm: https://github.com/daltoniam/zlib-spm/compare/master...c-bata:support-spm4?expand=1
• common-crypto-spm: https://github.com/daltoniam/common-crypto-spm/compare/master...c-bata:support-spm4?expand=1
• Starscream: https://github.com/daltoniam/Starscream/compare/master...c-bata:support-spm4?expand=1

There is a problem when sending a Pull Request to Starscream because C header files are moved inside include directory to support Swift PM v4 cause of constraints to support C language targets (See https://github.com/apple/swift-package-manager/blob/master/Documentation/Usage.md#c-language-targets for more details). So maybe Starscream builds in XCode will be failed cause of changing directory of header files.

[c-bata]

I bumped into a problem when building on Linux(dockerhub) :sob: CommonCrypt is only available at iOS/Mac. https://github.com/daltoniam/Starscream/pull/454

[harryjburr]

Yeah. That is true