dns: 'when' argument to mowgli_timer_add is relative to now
json: Generalize seralization interface

This interface allows users to optionally bypass the intermediate
serialization step to mowgli_string_t, and have mowgli.json call a custom
append and append_char callback.
Update jsontest example for the new serialization interface
Alter format of ll_table initializer

A GCC bug in certain versions of GCC for OS X prevents this type of
initializer from being parsed correctly.