GUID for the Assembly is only required if it's to be made visible for COM
The facility is optional from the client and should be set to GELF by the server if not present
Facility for the GELF message can now be configured for the appender.

By default we won't be setting a facility but it can be declared. This is more in-line with how syslog would work
and provides the flexibility to distinguish different logging applications
The Facility change probably warrants version upgrade
Facility appender property is now included in the sample config
Actually, the default for ComVisible is TRUE so we need to keep this as false.
Merge pull request #1 from mfloryan/facility

Facility
Cengiz : added necessary using for comvisible attribute