[SPM] Add support for swift package manager

[havocked]

Feature

Swift Package support

Motivation

We would like to add FiskalySDK framework with Swift Package Manager.

Pitch

Swift Package is getting increasingly more attention by developers. This PR shows that it's possible add this support without too much efforts and can benefits everyone!

What's going on?

• We add Package.swift manifest at the root of this repo so we can request the package directly the url: https://github.com/fiskaly/fiskaly-sdk-swift
  • Package.swift works very well with the following binary .xcframework.
  • We can easily generate it like you do with generateFramework.sh with this new script: generateXCFramework.sh

How to improve this PR

• We can modify to generateXCFramework.sh to generate a .zip file like so you can upload it and have a reference in the cloud
• Modify Package.swift to point at the uploaded .zip file url
• Remove the .xctframework

Notes:

~In FiskalySDK.xcodeproj/project.pbxproj, I've excluded arm64 architecture for iphone simulator in order to build, because I'm using XCode Version 12.2 (12B45b)~

~Debug/Release config:~ ~"EXCLUDED_ARCHS[sdk=iphonesimulator*]" = arm64;~ I had to remove this flag in order to pass CI

[havocked]

For now it works with XCode 11.3 for testing. But if using, later XCode version (12.2 for ex.), building will fail because of missing build settings: EXCLUDE_ARCHS -> ARM64