Closes#30
Introduces the "challenge" field in bot rule definitions:
```json
{
"name": "generic-bot-catchall",
"user_agent_regex": "(?i:bot|crawler)",
"action": "CHALLENGE",
"challenge": {
"difficulty": 16,
"report_as": 4,
"algorithm": "slow"
}
}
```
This makes Anubis return a challenge page for every user agent with
"bot" or "crawler" in it (case-insensitively) with difficulty 16 using
the old "slow" algorithm but reporting in the client as difficulty 4.
This is useful when you want to make certain clients in particular
suffer.
Additional validation and testing logic has been added to make sure
that users do not define "impossible" challenge settings.
If no algorithm is specified, Anubis defaults to the "fast" algorithm.
Signed-off-by: Xe Iaso <me@xeiaso.net>
d3e509517c