chore(project):swift4.2

- Added Swift Package Manager support for Swift 3 and Swift 4
- Updated `travis.yml` to latest `osx image` and devices
- Updated `SWIFT_VERSION` in all targets to `4.0`
- Updated CHANGELOG.md

chore(travis):update

- Set iPhone 7 Plus OS to 10.1 for Travis CI test
- In CDMarkdownHeader make sure `withSize` is used for all platforms

chore(project):swift4

- Updated swift version macro check and call appropriate methods for Swift 3.2

chore(changelog):update

- Updated README.md
- Updated CHANGELOG.md
- Updated podspec