Add initial stub for /blacklisted resource
Allow blacklist check to be executed against many

Now it is possible to configure multiple rbls to check against.
Simplify app configuration

Now environment variable names get deducted automatically.
Add more rbls

Made the query tolerate errors better. If the service is down or
something goes wrong, we assume that the ip is not on the rbl.

Note that we can make this query much nicer still. It could be nice to
return the names of the lists on which the ip is rather than returning a
boolean result. At least this is a start.
Return dns and name of rbls in case blacklisted

Way more user friendly this way.
Document blacklisted resource
Fix typos