* 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
* apollo-server-core: add file upload hooks and configuration
* apollo-server-core: make requestOptions and fileUploadsConfig public fields in ApolloServerBase
* apollo-server-express: initial fileuploads middleware
* apollo-server-hapi: initial file uploads middleware
* core: remove fileuploads from constructor and add merge capabilities
* express: add fileuploads to registerServer and single test
* hapi: add fileuploads schema merge to registerServer
* express: add check for EPIPE and ignore it due to upload server issue
* core: add scalar Upload to server construction