Support alternative separator to dot notation

[adatzer]

At the moment, the tag always supports dot notation both for getting event data and for setting request body properties.
As also discussed in the 0.1.0 pull request, it is not currently possible to support generating a request body where keys contain special characters.
It would be great if we could support escaping special charactes, like . for the destination mapped keys, which would allow for even more customization options.