Initial commit
Added .for_values ValueObject class factory method

* Version bump to 0.2.0
Updated gemspec
Added #empty? method
Update README.doc for #empty?
Version bump to 0.3.0
Implement ActiveModel attributes protocol

* #attributes: hash with string keys
* #attribute: alias for :[]
* Version bump to 0.4.0
Added ::value factory method

* Constructs completely immutable (frozen) values
* Version bump to 0.5.0
Updated Readme for 0.4.0, 0.5.0

* Version bump to 0.5.1
Rename to ValueStruct to avoid name conflict