Ruby

[DOC] Revisions for call-seq in doc guidelines (#6121)

Splits certain guidelines for singleton and instance method. Calls for instance method to not prefix anything (like RDoc itself for a Ruby-coded instance method); e.g.: count -> integer, not array.count,. <=> other -> integer or nil, not hash <=> other -> integer or nil. Groups previous guidelines into Arguments, Block, Return types, Aliases.