We recommend the use of apollo-engine-reporting and the other built-in features
of AS 2.0 rather than engineProxy. You can still use the apollo-engine npm
module manually with AS 2.0, or stay on AS 1.0.
* feat: ApolloServer is created and exported by all variants
* docs: add initial docs around exporting ApolloServer
* feat: export gql from integrations
* docs: change apollo-server examples to use express with registerServer
* server: remove registerExpressServer
* core, docs: comment functions, fix api reference, context creation more like middleware args
* docs: fix integrationed typo
* core: add test for context as async function
* core,express: add support and test of context as async function
* Update apollo-server.md
Fix style for `registerServer`.
