Create packages for easy installation

[richardtop]

Hi, it's a nice library.
However, it seems that it's not currently available as the package for Swift Package Manager or via CocoaPods, so that the library could be easily integrated with the application target.
Supporting both would serve multiple purposes:

• Makes it easier to integrate with the applications
• Keeps the library code separate from the app code
• Makes it very easy to upgrade to new versions of BlurHash
• Assists discovery

I recommend creating a library definition files (.podspec and package.swift), so that the library could be integrated with the dependency management tools.

[DagAgren]

Realistically speaking, most people would use the simple single-file implementation, which I am also not expecting to make any significant changes to in the future. I'm not sure a package manager actually adds much value here over just copying a single file.

I might still do it just because people are used to it though.

[kiliankoe]

I've copied the current implementation into a new repo to facilitate integration with SwiftPM here: https://github.com/niochat/BlurHash

I didn't open a PR here since SwiftPM relies on having a manifest present at the repo root, not a subdirectory and there wasn't any precedence here for other package managers.

It adds both the simple BlurHash implementation and BlurHashKit as targets that can easily be added to your app from within Xcode.

[EvanHahn]

Would you accept a PR to add CocoaPods support? If so, I might give it a try.