Better docs for Object#<=>

ri Object#<=>

= Object#<=>

(from ruby site)
------------------------------------------------------------------------------
  obj <=> other -> 0 or nil
   

------------------------------------------------------------------------------

Returns 0 if obj === other, otherwise nil.

The <=> is used by various methods to compare Objects, for example
Enumerable#sort, Enumerable#max etc.

Your implementation of <=> should return one of the following values: -1, 0,
1 or nil. -1 means self is smaller than other. 0 means self is equal to other.
1 means self is bigger than other. Nil means the two values could not be
compared.

When you defined <=>, you can include Comparable to gain the methods <=, <,
==, >=, > and between?.

The first commit is the docs as of ruby-1.9.3-p385

@apeiros Thanks! This change landed in r39414