consider use node's vm module instead of eval when using fromJSON

[bjrmatos]

no need to add details for why eval is evil so i think a better solution and more safety is to use the vm module.

example implementation (it works):

RuleEngine.prototype.fromJSON = function(rules) {
        var sandbox = {
            condition: undefined,
            consequence: undefined
        };

        this.init();
        if (typeof(rules) == "string") {
            rules = JSON.parse(rules);
        }
        if (rules instanceof Array) {
            rules = rules.map(function(rule) {
                sandbox = {
                    condition: undefined,
                    consequence: undefined
                };

                vm.runInNewContext("condition = (" + rule.condition + ")", sandbox);
                vm.runInNewContext("consequence = (" + rule.consequence + ")", sandbox);

                rule.condition = sandbox.condition;
                rule.consequence = sandbox.consequence;
                return rule;
            });
        } else if (rules !== null && typeof(rules) == "object") {
            vm.runInNewContext("condition = (" + rule.condition + ")", sandbox);
            vm.runInNewContext("consequence = (" + rule.consequence + ")", sandbox);

            rule.condition = sandbox.condition;
            rule.consequence = sandbox.consequence;
        }
        this.register(rules);
    };