Hardening/136

Implements the issue https://github.com/telefonicaid/fiware-connectors/issues/136

Additionally, minor modifications have been done in the main README regarding missing Flume event headers.
o Please notice <b>that</b> the `process` method handles all the possible errors <b>that</b> may occur ...
o specially => especially <i>(actually, 'specially' exists also but is practically never used)</i>
o There <b>exists</b> a collection of Cygnus-related exceptions <b>whose</b> usage is mandatory<b>,</b> located at: