Resurrect Dobby

[bkempner]

Updated to swift 5 and added SPM support. I also fixed what I think was a minor oversight, which was that a Dobby.matches(_ value: Value) method is missing, this seems to prevent me from creating mock methods which take a single non-collection type argument, unless there was some other way of doing this that I couldn't figure out.

I realize Dobby hasn't been maintained in a while, but I did this for my own project so thought I would make it available to others.