The EDNS response code part only contains 8 bit so the return type fits its
need better. This aligns the type with `ResponseCode::from` and
`Edns::set_rcode_high`.
Closes#1202
* in honor of Juneteenth, remove replace Master with Primary
* in honor of Juneteenth, remove replace Slave with Secondary
* add 8499 for reference about naming
* clean up deprecation warnings
* remove unsupported markdown strikethroughs...
* revert primary to master in BIND compatibility tests
* all tests updated for new background
* background in Resolver now supported, wip
* clean up client impls
* client passing all tests
* cleanup review comments, remove try_locks
* remove mutexes on NameServers in NameServerPool
* refactored ConnectionProvider
* remove pinutils dependency
* remove the now unused custom *LookupFutures
* remove unused types
* remove all deprecated interfaces from Client
* rename ClientFuture to AsyncClient
* all clippy warnings and SecureClient working
* cleanup clippy warnnings
* Everything working with Background removed
* fix infinite loop
* Client refactored without background
* rebased onto tokio 0.2
* remove Clone and Option from background connects
* cleanup from review
* fix clippy warnings
* spawn in ConnectionProvider
* fix no-default-features test
* only expose testing functions during testing
* fix copyright typo
* revert lookup_ip interface change
* limit tokio features to least required set
* rename tokio-compat to tokio-runtime
* use async fns where possible on AsyncResolver
* fix lifetime issue
