Update documentation for filters.

docs/simplesamlphp-authproc.txt

modules/core/docs/authproc_attributeadd.txt

modules/core/docs/authproc_attributelimit.txt

modules/core/docs/authproc_attributemap.txt

modules/core/docs/authproc_attributerealm.txt

modules/core/docs/authproc_generategroups.txt

modules/core/docs/authproc_languageadaptor.txt

modules/core/docs/authproc_php.txt

modules/core/docs/authproc_scopefromattribute.txt

modules/core/docs/authproc_statisticswithattribute.txt

modules/core/docs/authproc_targetedid.txt

modules/core/docs/authproc_warnshortssointerval.txt

modules/core/lib/Auth/Process/GenerateGroups.php