Tweaks to new Wrapperless mode

[joshwcomeau]

Some small tweaks to @tobilen's excellent work creating a wrapperless mode for React Flip Move with React 16.

• Removed the anchor, as this will be computed based on the parent
• Removed the warning for not supplying an anchor
• Update README
• Add details to API reference
• Fix bug with the first transition being buggy, by setting the parentData on mount
• Extract findDOMContainer method
• Switch from false to null for typeName
• Update flow-typed defs
• Update package.json version number