* Support fields resolvers #25

* Code coverage for MappingConfig #25

This makes use of the MultiSourceReader provided by the graphQL library.
Using this reader allows to read a single document from multiple files,
while correctly associating line numbers and errors to their original
source file.

This doesn't bring any overhead because the method Parser.parseDocument(String) that was previously used already created a MultiSourceReader itself.
Note that the previous method didn't associate the source file name with the content used for parsing, while the new one does.

It allows to solve cross-reference problems with union types for instance.

Resolves:
https://github.com/kobylynskyi/graphql-java-codegen/issues/27Co-authored-by: NJoffrey Bion <joffrey.bion@booking.com>

* Cleanup imports/generics

* Remove residual trim() from previous PR

* Add utility function to compare file contents ignoring trailing whitespace
Co-authored-by: NJoffrey Bion <joffrey.bion@booking.com>

* Support for async resolvers

Solves issue: https://github.com/kobylynskyi/graphql-java-codegen/issues/24

* https://github.com/kobylynskyi/graphql-java-codegen/issues/24 Refactors and fixes

* Renamed asyncApi to generateAsyncApi in MappingConfig
* Changes for adding java.util.concurrent import when it comes to async Query or Mutation
* Improved tests coverage

The GraphQL specification says that Float type is double-precision.
It is thus effectively equivalent to Java's float.

Resolves:
https://github.com/kobylynskyi/graphql-java-codegen/issues/22Co-authored-by: NJoffrey Bion <joffrey.bion@booking.com>

* Add default values generation

* Avoid using List.of() to keep java 8 support
Co-authored-by: NJoffrey Bion <joffrey.bion@booking.com>

* Introduce model annotations (for Lombok) #10

* Unit tests for MappingConfig

* Remove unused import in MappingConfig

* Remove code related to modelAnnotations

* Handle DirectiveDefinition in GraphQLDefinitionType determiner

* Adding a catch handler in case there are other types we can't handle

* Fixing typo from last commit