Replacing __defineGetter__ and __defineSetter__ with Object.defineProperty get and set

Replacing Node.prototype.p
Replacing __defineGetter__ and __defineSetter__ with Object.defineProperty get and set

Adding get and set for Node.prototype.fixed
Adding set to Node.prototype.tempMass
Adding get and set to Node.prototype.mass
Merge pull request #1 from joedborg/defineGetterAndSetterFix

Replacing __defineGetter__ and __defineSetter__ with Object.defineProperty get and set