Pluggable per-table handlers for event processing.

Pluggable per-table handlers for event processing.

1. Make handler modules known for Londiste:

  [londiste3]
  handler_modules = londiste.bublin, some_other.module

Modules are imported and classes found in __londiste_handlers__
module variable are registered.

2. Generic table setup:

  londiste3 cf.ini add-table foo --handler='handler1' --handler='handler2(arg1, arg2)'

Londiste standard handler is default and always appended to custom plugins.