Improve apache_error format
Merge pull request #412 from y-ken/parser_apache_error

Improve apache_error format
Implement 'disable_retry_limit' output option.

Setting 'disable_retry_limit' causes 'retry_limit' to be ignored
in favor of retrying forever.  This implicitly disables any
secondary output configuration as well.
Merge pull request #415 from salty-g/master

Implement 'disable_retry_limit' output option.
Refactoring of SetTagKeyMixin and SetTimeKeyMixin.
Merge pull request #411 from baschtl/better-configurable-time-key-and-tag-key-mixins

Refactor time key and tag key mixins
Implement Label feature
Replace Engine.emit with router.emit
Add filter feature
match and filter should be initialized with mix order
Output provides router attribute to emit event stream