Backlog/112 alarms

Adds an Alarm document, finishing the issue https://github.com/telefonicaid/fiware-connectors/issues/112

It also adds new INFO traces needed by the alarm system.

A minor fix in the README has been done as well.
I think it is OK :) I want to say "events" in plural. Maybe I can rewrite it as: "...which works as a temporal buffer for events that have not been processed yet".