Class attribute rules

[meisyal]

The current version of staruml-ruby (0.1.4) supports these class attribute rules:

1. If an attribute is set to no readonly and no static, an instance variable is generated and uses attr_accessor :attribute_name.
2. If an attribute is set to readonly and no static, an instance variable is generated and uses attr_reader :attribute_name.
3. If an attribute is set to no readonly and static, a constant is generated.

In the future release, there are some modification for those rules:

1. A constant is generated if the attribute is set to readonly and static.
2. A class variable, @@attribute_name, is generated if the attribute is set to no readonly and static

[meisyal]

This feature has been implemented in release 0.1.5.