Improve runtime performance

[tobiasgirardet]

Right now, DeidentiFHIR works like this:

1. Iterate over all elements in a given FHIR resource
2. Check for each element if it should be removed/handeled by looking for handlers in a hash map using the current elements path

If we put the handlers in a tree structure, where each connection represents a step in the FHIR path, we can omit whole sub trees of a resource if no handler is registered at all.

[tobiasgirardet]

However, keep in mind that some checks can only be performed on the leave nodes during runtime.