Demo is unhelpful for reporting crash bugs

[not-an-aardvark]

When the demo is initially loaded with code in the URL that causes ESLint to crash, it logs an error to the console and the UI remains at the "loading" screen indefinitely without ever displaying the code. Similarly, if the code in the demo is edited to something that causes ESLint to crash, the permalink doesn't update in the URL bar.

This makes it difficult to use the demo to debug and report crashes, because (a) the demo won't generate a permalink URL for code that causes ESLint to crash, and (b) even if a permalink URL is generated manually, it won't be possible to load the URL.

I think it would be nice to catch these errors and display a linting message like "ESLint crashed, see the console output for more details".