I like the way Array.from works. It takes any iterable and casts it to array.

As discussed in #317 - we have to deprecate toMap, toList, and etc. methods, but we also need a good replacement for it.

We can do this in constructors - but immutable class constructors returns values in it, which is restricted in es6 classes spec and sooner or later people will start to demand untranspiled ES6 module version for modern browsers.

And as a summary:

1. Implement #from(iterable) for each method.
2. Add deprecation warnings for toCollection methods.