The closure created by the `onExited` handler prevented the previous
child from being cleaned up; this could cause chains tens of thousands
of elements long, consuming ever more memory as the application ran.

Fixes #219

Replace Transition

* Fix CSSTransition codesandbox example 

Old:
https://codesandbox.io/embed/yv645oq21x

New:
https://codesandbox.io/embed/kw8z6pp9zo

* Accidentally removed line

* render only children with component=null

* update jsdocs for component=null

* lint

…ed (#257)

Update documentation

…ransition is rendered as null (#208) (#270)

* Add -done class names

* Remove done classes on transition

* Add additional documentation for -done classes

Different was not as clear to me -- these are not backward compatible. 
Technically semantic versioning implies this, but it's better to be explicit.

* Ignore Visual Studio Code configuration in git

* Add .yml extension to ESLint config files

They are already written in YAML format, so this gives us syntax
highlighting.

* Fix ESLint errors in documentation files

* Implement Prettier through ESLint

Currently only for documentation files.

* Split components into pages

- use react-bootstrap to add navigation
- auto-generate component pages using Gatsby Node API

* Fix transition state names in the docs

* Update CodeSandbox examples

* Document CSSTransition's reflow hack