Added pifu_absence

Added pifu_absence element to PIFU-IMS_SAS schema
Added pifu_absence element to xsd
Added absence examples for PIFU-IMS
Done XML format and indent with oXygen
Changed result types to english
Added group information for the school

In this example all referenced groups have to be included
Moved absence for a spesific subject to the membership information of that subject
Updated description of sourcedid in absence
Split up grade and absence examples

Split up grade and absence examples into seperat example files
Split up of grade and absence examples

Split up of examples with grade and absence info; also corrected
comments on example 1.
Example 2 has absence_id for both aggreate and occurence absence.
Changed a few search-replace typos
Merge pull request #3 from bbjonnes/master

Added absence in schema and examples