default option fix

[loadkpi]

fix #19

[frvade]

1. writer: false removes any opportunity to actually write anything to the attribute. So with this option enabled you must override reader to simulate attribute. Private writer combined with excluding private writers from mass-assignment will solve the problem without having to simulate the attribute behaviour. In any casedefault: setting should work with writer: false.
2. reader: false disables any way to read the attribute. Why anyone would use it? What if I want to read it inside the instance? To make mass-assignment work with a pseudo-attribute which will set other attributes we can just make the reader private. We will have a reader inside an instance and with the proposed changes it will not show up in the attributes.