SwiftPM support

[c-villain]

Add the ability of including dependency via Swift Package Manager

[odrobnik]

@c-villain Why don't you add a pull request for that?

[odrobnik]

Ok, I implemented SwiftPM support, including testing. Now it builds with

swift build

and tests with

swift test

Would you please test it from the current develop branch and give feedback. It should work perfectly, but sometimes there's something missing that only appears on another person's machine.

cc: @marcmatta @c-villain

[odrobnik]

cc:@aromanov91 @skelet2394 @bigimot22 @Exey

[marcmatta]

@odrobnik all looks perfect from my side.