function setReadWriteAccessor( obj, prop, getter, setter ) {
	defineProperty( obj, prop, {
		'configurable': false,
		'enumerable': true,
		'get': getter,
		'set': setter
	});
}
Defines a read-write accessor.

@param {Object} obj - object on which to define the property
@param {(string|symbol)} prop - property name
@param {Function} getter - get accessor
@param {Function} setter - set accessor

@example
function getter() {
    return name + ' foo';
}

function setter( v ) {
    name = v;
}

var name = 'bar';
var obj = {};

setReadWriteAccessor( obj, 'foo', getter, setter );

var v = obj.foo;
// returns 'bar foo'

obj.foo = 'beep';

v = obj.foo;
// returns 'beep foo'