Fix support for using withUrqlClient with _app.js.

[parkerziegler]

Fix #6

Thanks to @bmathews for finding the needle in the haystack and getting this working 🎉 Ultimately, the issue here had to do with how the withUrql HoC received the urqlClient from getInitialProps. In the case where we were wrapping a Page component, this was working as expected. getInitialProps would get run, we'd run ssrPrepass on AppTree (in this case, our Page component), and the urqlClient would get passed down via props. ✅

With _app.js however, things are a bit different. The urqlClient we attach to pageProps is no longer a direct page prop b/c what we're wrapping isn't a Page component, it's the full App component. _app.js gets access to each page's props via pageProps rather than direct props. So, in cases where we wrap _app.js, we need to check pageProps.urqlClient.

This change is in withUrqlClient, which is the only really important file to review. Otherwise, the changes here are just expanding our example directory into an examples directory. It's the same app, but one the first wraps a single Page component while the latter shows how to use next-urql with _app.js. Fortunately for us again, there's no breaking API change in this PR, so we can release this as 0.2.3 🎉

[kitten]

Awesomeeeeee! ✨👏 we’ve been struggling to narrow this done for a while! Happy to see that this is finally a solution for both approaches/camps of how to use urql with Next!

[JoviDeCroock]

Nice one 🎉