* Add BadUserInputError and TransientError as extensions of ApolloError
* remove TransientError
* update test so that properties end up under `error.extensions.exception`
* update documentation to talk about BadUserInputError
* check for properties after formatApolloErrors has been called
* fixed highlighted lines for docs
* export BadUserInputError from `apollo-server`
* fixed highlighted lines for docs
* export BadUserInputError from `apollo-server`
* update changelog