lib/ostruct.rb: [DOC] revise docs for OpenStruct
* update paragraph on implementation:
define_singleton_method is used, not define_method
* add call-seq with return values for each_pair
* adopt description of dig from Array and Hash
* fix description of the hash method
* :nodoc: initialize_copy, respond_to_missing?
* other small improvements, e.g. use the term `attribute' in the docs
(instead of `member'), which is clearer for users of the class
* improve code examples: e.g. use more consistent style (always use
double quotes, drop `p' and `puts', ...), update inspect output,
use example data that is not prone to change (like population)
* add more code examples
* fix some small errors and grammar
[ruby-core:79265] [Bug #13159]
merge revision(s) 57887: [Backport #13159]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_2@58124 b2dd03c8-39d4-4d8f-98ff-823fe69b080e