Rewrite in Swift as a Swift PM package

[friedbunny]

Fixes #2 by rewriting in Swift as a Swift PM package. This necessarily switches from a bundled plist to an inline dictionary of coordinates, as SPM currently does not support bundled resources.

To-do

• Rename project “TimeZoneCoordinate”
• Verify Obj-C interoperability.
• Clean up remaining Obj-C implementation details.
• Test performance of TimeZoneCoordinates dictionary and investigate alternatives.
• Update podspec and verify.
• Fix import script so that it updates Coordinates.swift.
• Write other tests.
• Update readme.

[OdNairy]

Hey @friedbunny
Is there any chance of merging the PR? 🙂