Implement Default for EventLoopConfig
Implement Default for EventLoopConfig

Closes #284

rrichardson/mio,dwrensha/mio,carllerche/mio,asomers/mio,fuchsia-mirror/third_party-mio,fuchsia-mirror/third_party-mio,asomers/mio,arthurprs/mio,murarth/mio,mneumann/mio,danburkert/mio,carllerche/mio,mneumann/mio