Fix retain cycle

Merge pull request #23 from steamclock/jc/22-fix-retain-cycle

[22] Fix retain cycle

Migrate to Swift 4.2

• No code changes needed in this migration
• Updated configurations in Xcode, podspec, readme, and changelog to make all Swift version specifiers point to 4.2

Better Switcher Active Endpoint Icon

Improved the UI for showing the active endpoint in the switcher.

Add custom actions

Added support for custom actions within Switchcraft!

0.1.2

Added a fallback for if CFBundleDisplayName is nil.

Add build information to switcher

Changed the default alert message from nil to contain the version and build number.