Added note to WeakMap and WeakSet results

WeakMap and WeakSet constructor arguments, such as new WeakSet([obj1,
obj2]), are not supported in most browser platforms.
Added a further note to Map and Set results

Additionally, it seems only Firefox supports arguments to the Map() and
Set() constructors.
Merge pull request #208 from webbedspace/weakmapnote

Added note to WeakMap and WeakSet results