Immutable.fromJS should be proxied as well #3

Hi!

The problem is that many people ofter convert values from vanilla data to Immutable objects using fromJS and you don't get the immutable-proxy features now when using that function which gives you a false feeling that everything will work right away with now additional code analysis. Actually, I've just spent more that 30 minutes to figure out what was wrong with my code.

My proposition is to "trap" the fromJS method as well.

Docs: https://facebook.github.io/immutable-js/docs/#/fromJS
Sources: https://github.com/facebook/immutable-js/blob/master/src/fromJS.js

It seems it'd be really trivial to trap it (with, perhaps, a bit of copy-paste).

What do you think?

Thank you!

P.S. I can implement it myself if the idea sounds good for you.