Update README.rdoc

Update Singleton section of Readme, to accord undocumented yet changes (https://github.com/josevalim/inherited_resources/commit/cfb2d88c6d93dbaf9bd4a81996a660181fd2b2e1 - Allow for nesting of singleton belong_to's.)
allow permitted_params to be a private method

The examples in the strong_parameters README show a private method
for parameter sanitization.  This tiny change allows for following
that pattern.
typo fix
Don't call :scoped if it's deprecated.
Merge pull request #272 from tab/master

typo fix
Merge pull request #271 from rubysolo/allow-private-method

allow permitted_params to be a private method
Merge pull request #269 from iantropov/master

Update Singleton section of Readme
Minor indentation fix
Merge pull request #274 from lnakamura/master

Minor Readme indentation fix
test changed so that permitted_params are tested in case it's private (regression test)
Unsplatting simplified
caching refactored to @var||= begin ... end form
Merge pull request #278 from prijutme4ty/caching_refactored

caching refactored to `@var ||= begin ... end` form
Merge pull request #277 from prijutme4ty/test_private_permitted_params

test changed so that permitted_params are tested in case it's private (r...
Merge pull request #273 from dougo/rails-4-deprecation-warning

Don't call :scoped if it's deprecated.
Merge pull request #279 from prijutme4ty/simplified_unsplatting

Unsplatting simplified
Using release candidates of responders and has_scope gems
class_methods.rb: update documentation for to match newer code
Merge pull request #282 from Rio517/master

Small documentation fix
Use a safer check for :scoped being deprecated.

This works even if ActiveRecord is not defined.