wr currently uses fs.watch() to watch for file changes. Unfortunately, there is some kind of OS limit on the number of files that can be watched per process, or something. We should provide a command-line option to use the stat-based polling method fs.fs.watchFile() instead. May need to provide an option for the polling interval as well; perhaps that's the value of the command-line option "--poll" or something.
add polled watching option, fixes #5