Added a Swift implementation of SiriWaveformView

[Felizolinha]

I implemented your SCSiriWaveformView in Swift, I thought it would be cool to share it here as others might need it!

[stefanceriu]

Hey, thank you for raising this pull request.

Although swift is cool and whatnot I don't really see a reason for it to be part of this repository though. I would suggest you create your own separate repository and make it its own project.

In the mean time, I'm going to leave this pull request open just in case anybody needs a swift version.