Now they are represented by implementations of the log.Output interface
instead of just callbacks. This allows to add additional methods to it.
Mainly, it was done for purpose of Close method for flushing and closing
log files. This is important to make runtime logger reinitialization
(e.g. log rotation) possible.
Additionally, documentation now explains goroutine-safety of logger
objects.
Check.NewMessage is renamed to Check.CheckStateForMsg to allow
a single module to implement both Modifier and Check interfaces.
Due to various implementation details, body and MAIL FROM rewrites
are not applied on per-destination basis.
Closes#134.
Root package now contains only initialization code and 'dummy' module.
Each module now got its own package. Module packages are grouped by
their main purpose (storage/, target/, auth/, etc). Shared code is
placed in these "group" packages.
Parser for module references in config is moved into config/module.
Code shared by tests (mock modules, etc) is placed in testutils.
