0.7.0 2018-08-10

• Allow returning errors from resolve function of io_field (#69)
• Support for union and interface types (#70)
• Expose HTTP request to context construction function in Graphql_lwt.Server.start (#88)
• Fix error response from Graphql_lwt.Server (#96)
• Allow passing operation name to Graphql_lwt.Server (#103)
• Querying undefined fields gives validation error (#105)
• Fix parsing of enums with E (#109)