Filesystem monitoring support for nio4r

by Upekshe Jayasekera for Ruby

Both libev and Java NIO2 have APIs for evented filesystem monitoring. However, nio4r does not presently expose these APIs into Ruby. This project would involve creating an abstract filesystem monitoring API that interacts with NIO::Selectors in a generic way and exposes the some API on both CRuby and JRuby. This would allow filesystem monitoring within the same event loop as other nio4r events