in this commit:

- centralize logging output handler.
- set global Info/Debug/Error log levels based on config file or flags.
- remove per-plugin debug arg handling.
- add a I!, D!, or E! to every log message.
- add configuration option to specify where to send logs.

closes #1786

* Add mandrill webhook.

* Store the id of the msg as part of event.

Signed-off-by: Cyril Duez <cyril@stormz.me>
Signed-off-by: François de Metz <francois@stormz.me>

* Decode body to get the mandrill_events.

Signed-off-by: Cyril Duez <cyril@stormz.me>
Signed-off-by: François de Metz <francois@stormz.me>

* Handle HEAD request.

Signed-off-by: Cyril Duez <cyril@stormz.me>
Signed-off-by: François de Metz <francois@stormz.me>

* Add the README.

Signed-off-by: Cyril Duez <cyril@stormz.me>
Signed-off-by: François de Metz <francois@stormz.me>

* Add mandrill_webhooks to the README.

Signed-off-by: Cyril Duez <cyril@stormz.me>
Signed-off-by: François de Metz <francois@stormz.me>

* Update changelog.

Signed-off-by: Cyril Duez <cyril@stormz.me>
Signed-off-by: François de Metz <francois@stormz.me>

* Run gofmt.

Signed-off-by: Cyril Duez <cyril@stormz.me>
Signed-off-by: François de Metz <francois@stormz.me>