* 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:

Re-organize page docs

These two class are most common sources of infinite sequences.  This change should effectively prevent accidental infinite loops when calling to_set on them. [Bug #21513]

Small correction to the Range docs. All beginless (nil..) and endless (..nil) ranges, as well as fully open ranges (nil..nil), display "nil..nil" when inspected, regardless of their original syntax.

Infinite ranges, i.e. unbounded ranges, should overlap with any other range
which wasn't the case in the following example: (0..3).overlap?(nil..nil)

When the end points of an inclusive range equal, `Range#step` should
yields the element once.