This should help monitor the use of the link shortener, in particular
for nefarious uses.
Prompted to do this by https://app.y.gy/blog/honeypot
This addition included some minor refactoring.
Of note, is that, previously, every field was required to be defined in
`config.json`. The creation of field-specific types plus the inlcusion
of `#[serde(default)]` does away with this.
Also fixed debug message on config.json version mismatch.
meeg_leeto