Removing .swiftpm folder

Update README

Updates to the README as per recommendations by Dave Verwer on Twitter - https://twitter.com/daveverwer/status/1042753811813679105

Update README.md and project versions.

Added bounding box shrinking method.

Renamed API to remain consistent and refactored the Bounding Box struct to use variables instead of methods for clarity over immutability

Separated the unit tests into different files for better clarity

Added diagonal distance computed value for bounding box type

Fixed target structure and shared test scheme.

Code coverage is 100%

Added public memberwise initialiser as it defaults to internal

Added README and switched shared schemes to release configuration