Grammatical edits only.
Merge pull request #247 from deb-cfengine/user_ptype

Grammatical edits only.
manuals/language-concepts/classes.markdown: explain no whitespace is allowed

Suggested in https://cfengine.com/dev/issues/3779
Redmine#3578: document cache_system_functions and mention execution model
truthiness: clarify how boolean function can return a string
Merge pull request #248 from tzz/master

document cache_system_functions and more