Add: Documentation of new option to disable cf_promises_validated

Ref: https://dev.cfengine.com/issues/6688
Don't merge without: https://github.com/cfengine/masterfiles/pull/340
Add: History when persistence was added to classes promises
Merge pull request #949 from nickanderson/persistence_added

Add: History when persistence was added to classes promises
Merge pull request #948 from nickanderson/option_cf_promises_validated

Add: Documentation of new option to disable cf_promises_validated
adjust timelines
Change: Fix missing link reference
Merge pull request #951 from nickanderson/fix/docs

Change: Fix missing link reference
clarify variablesmatching() semantics, asked by user
user creation dependency
install instructions for solaris and aix
Redmine#6725: add tag documentation for classmatch() and countclassesmatching()
Merge pull request #952 from tzz/tzz/redmine6725-tagify-class-matching-functions

Redmine#6725: add tag documentation for classmatch() and countclassesmatching()