Always return 'this' from Thorax.View.render().

[ryan-roemer]

Backbone's view.render() says:

    // **render** is the core function that your view should override, in order
    // to populate its element (`this.el`), with the appropriate HTML. The
    // convention is for **render** to always return `this`.
    render: function() {
      return this;
    },

However, Thorax.View.render() returns undefined if there is no view.el and the output parameter passed to render() in the other case. This PR switches both cases to return this per the Backbone way.

Note: This is technically a breaking change for anyone who relied on output being passed pack in a chain of some sort. I believe that behavior is completely undocumented, but I'm not sure what the expectations are in that regard.

/cc @kpdecker @eastridge

[eastridge]

@kpdecker I'm ok with this on WWW side and core library. Does this work for you in mobile land or do you want me to run unit tests? Do you have a regression testing strategy beyond that in place for a branch like this that is more formal?

[kpdecker]

I think our return value strategy was a bit screwy to begin with so this is a "bug fix" but lets hold off on releasing it immediately. If this is released in 3.0 vs. 2.x.x then all the better for breaking concerns.

[kpdecker]

Released in 2.3.3