[Umbrella] The new urql monorepo

[kitten]

Summary

All of urql, including its separate packages have now been moved to this repository. This is a move towards a monorepo to make it easier to find and contribute to packages related to the urql ecosystem.

This doesn't mean that you have to install any different packages, but that their source will now live in this repository.

Changes

• All build tools and other scripts are unified and consistent between packages now.
• All packages will now live at urql/packages/* and all exchanges will be at urql/exchanges/* (This will give us the opportunity to relase more exchanges without the added maintenance burden!)
• CHANGELOG files will from now on be automatically kept up-to-date by the changesets tools to ensure that they're consistent (and present everywhere)

Where have things moved?

• The urql package will still be published as urql. In the monorepo however it's now located at urql/packages/react-urql.
• The urql/core entrypoint still exists in the package, but now points to a separate React-free package, @urql/core, which lives at urql/packages/core.
• @urql/preact and the WIP @urql/svelte now live at urql/packages/preact-urql and urql/packages/svelte-urql respectively and use @urql/core.
• @urql/exchange-graphcache is not at urql/packages/graphcache.

What changes for me?

• If you'd like to create issues, they'll now have to be created in this repository only.
• If you're interested in docs, they're now all in this repository as well. (Our website will eventually also move into this monorepo)
• If you're interested in contributing, there's now a brand-new CONTRIBUTING guide.

Will more packages move into the monorepo?

Yes! Eventually we'll move over the website, next-urql, add new exchanges (like retry and execute), and more!