mod_rest: Declare presence priority an integer in -128..127 per RFC6121 util.datamapper doesn't actually understand min/max, but it's informative and the schema could be used to validate the input at some point.

This module lets you block connections to remote servers at the s2s
level.

``` {.lua}
s2s_blacklist = {
    "proxy.eu.jabber.org",
}
```