* Document Range#to_set

* Update Thread#raise and Fiber#raise signatures and docs

* Add reference to String#strip to character_selectors.rdoc

* Update *nil docs when calling methods

* Enhance Array#find and #rfind docs

* Add a notice to Kernel#raise about cause:

[DOC] Rewrite argument unpacking docs and document **nil

Signed-off-by: crazeteam <lilujing@outlook.com>

* Per @nobu review

* Rdoc enhancements for Array

* Responses to review