Fixed memory leak

This release fixes a memory-leak that was uncovered by a few different users. Thanks again @bk-splunk!

Added QueryPlanCache infrastructure

Added plan cache (#79)

* added QueryPersister interface

* renamed PostBody to HTTPOperation

* organized thoughts on persisted queries

* added WithQueryPersister option

* fixed bug in WithQueryPersister

* renamed QueryPersister to QueryPlanCache

* added test for AutomaticQueryPlanCache

* test for persisted queries parameters through post body

* added test for query plan cache via get requests

* removed duplicate logic in graphql handler of get requests

* renamed persist files to cache

* cache retrievals kick off garbage collection

* actually debounce

* added test for WithNoQueryPlanCache

* more query plan cache tests

* fixed cache planner error test

* objectified inputs for gateway.Execute

* added mock executor

* field should be visible

* added cache key in response

* AutomaticQueryPlanCache will generate a hash if one is not given

v0.0.14: Fixed inline and spread fragments in federated queries (#80)

* Adds tests for inline and spread fragments with federation in
execution step
* Use nautilus/graphql v0.0.7

v0.0.13

fixed bug preventing client for asking for __typename (#73)

v0.0.12

http handler sends application/json as response (#71)

Fixed errors when using nested objects as variables

Small fixes for jakubknejzlik (#69)

* updated graphql library

* bumped graphql to 0.0.6

More graphql library bumps

v0.0.10

bumped version of nautilus/graphql fixes #68

v0.0.9

graphql version bump

v0.0.8

updated graphql module version

v0.0.7: Batching integration (#63)

* renamed NetworkQueryer to SingleRequestQueryer

* applying network middlewares works on any QueryerWithMiddlewares

* planner's QueryerFactory now takes the planning context

* renamed configurator to option

* added type declaration for queryer factory

* fixed comments

* added test for passing queryer factory

* cleanup

* comments

* more comment tidying