Provide graphql-tools functionality in Python

[Cito]

Creating executable schemas from SDL with GraphQL.js/graphql-core-next is possible, but grafting resolvers, custom scalars and enums manually into the schema after creating it with build_schema is cumbersome (see e.g. #20) and has a smell of monkey-patching.

The makeExecutableSchema function of graphql-tools provides a better solution.

We should consider porting this functionality to Python as well, either as a separate packare or as a subpackage of graphql-core-next.

[patrys]

You might want to take a look at https://github.com/mirumee/ariadne 😄

[Cito]

@patrys - thanks, wasn't aware that this existed. Nice! Will definitely look into that. Maybe it will suffice mentioning this in the documentation.

[Cito]

I have mentioned Ariadne now in the README.

[jberryman]

FWIW I arrived here because I was looking for functionality that could "prune" a schema by removing unreachable types, similar to what's offered in graphql-tools