Added new pifu_id-types in xsd

Added two new types of ID-numbers in pifu_id. municipalityNumber and
countyNumber.
Updated the schema version information
Added municipalityNumber and countyNumber to documentation and example
Updated an old url
Dummy change to enable documentation screenshots

No real change, just need a few screenshots to create documentation.
Added support for negative absence in pifu_absence_value

Added new type t_decimal8p4_wn and changed restriction base of type
pifu_absence_value to t_decimal8p4_wn. Problems related to validation
of negative absence.
Updated documentation with latest changes
Updated version number to PIFU-IMS 1.1
Updated version information in readme
Merge branch 'version-1.1'