Improve semantics logic to be more generic

[hugomrdias]

I've read through all of this, and it all looks great. I just have one suggestion (which may already be in the pipeline), which is that the logic in semantics.js could probably be made generic for any set of hierarchical actions. So it could be turned into something where maybe instead of a storageSemantics class, there could just be a generic semantics class. So you'd have:

const storageActions = {
  'upload/': {
    '*': {
      'IMPORT',
    }
  }
}

And then you could pass that into the generic semantics class like:

const storageSemantics = sematics(storageActions);

and the tryParsing and tryDelegating methods (and therefore that whole class) then become completely generic and can be used for other cases as well.

You've probably already thought of this, but it's my main suggestion for improvement at the mo.

Originally posted by @adamalton in #3 (comment)