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)