added examples of an xslt template for customizing email objects (both are commented out by default)

the first template is simpler and has no contents but just shows how the template match rule should work

the second template extracts the from header and uses this to print out some simple content
fixed problem where stixCommon:TTP were not being processed in the "reference" lookup.  Only stix:TTP were successfully processed.

this meant that a stix:TTP that had related TTPs with embedded stixCommon:TTP elements would not be properly processed.

This fixes issue #10