fix NIO deprecations & update to secure versions (swift-server#141)

add support for redirect limits (swift-server#113)

swift 5.1 docker setup (swift-server#111)

motivation: support swift 5.1

changes:
* add docker compose file for swift 5.1, will add CI job once merged
* update swiftformat version to 0.40.12

give generic parameters nice names (swift-server#99)

add NIO event loop as an argument for execute (swift-server#79)

* add NIO event loop as an argument for execute

* review fix: add to np-delegate method as well

* Resolve confict

* add missing linux test

* fix formatting

* missing self

* review fix: add event loop preference argument instead of eventloop

* formatting

* review fix: spelling

* fix compilation error

* review fixes: make preference argument not explicit and add precondition that EL must be part of ELG

remove unused degate and make other one public+rename (swift-server#61)