getterSetter
The getterSetter argument passed to registerConverter.
    Object
  
  An object with a get and set method that get converted to a two-way helper.
stache.registerConverter("numberToString", {
 get: function(fooCompute) {
    return "" + fooCompute();
 },
 set: function(newVal, fooCompute) {
    fooCompute(+newVal);
 }
});
A getterSetter object provides:
- A 
getmethod that returns the value of theleftvalue given the arguments passed on theright. - a 
setmethod that updates one or multiple of therightarguments computes given a newleftvalue.