Rewrite BindTo to support Type Conversion and Binding Hooks

[anaisbetts]

The main impetus for this PR is something like this:

this.OneWayBind(ViewModel, x => x.SomeModel.Text, x => x.SomeTextBox.Text);

The existing code will always attempt to set SomeTextBox.Text to null on startup because ViewModel is initially null in the View constructor, which WinRT will subsequently die on. This is because OneWayBind uses BindTo internally, which has the same bug.

However, when I dug into it, I realized BindTo was missing all kinds of things, and should have the same features. So let's do that

TODO:

• - Write a test to simulate the WinRT failure, then verify it's fixed.

[haacked]

This seems weird. Why not IObservable<TVProp> source; It doesn't require setting a default if all branches of the subsequent if statement set it before it's accessed, right?

[anaisbetts]

I'm trying a new style, where I just use var everywhere. Bart De Smet taught me that one.

[haacked]

Heh, ok. Interesting. That crazy Bart character.

[haacked]

I'm not going to pretend I understand all of this. :) Perhaps my only comment is I really do think the public methods should validate the parameters passed in. NullReferenceException doesn't carry much information when someone accidentally calls the method wrong either directly or indirectly.

[anaisbetts]

@haacked Yeah, you're probably right. Let's jump off that bridge later though :)