v0.4.0

New stuff

• Customizable and overridable <Document> (html).
• Updated documentation
• Add documentation about prefetch
• Add after test command. It works like CRA's / Razzle's.
• Add nicer experience if 3000 is in use already.

Breaking

• Remove razzle references from the codebase and docs. razzle.config.js -> after.config.js.
• .env variables now must start with AFTER_XXXXXX