ProxyFS proposal

[james-pre]

I just had this idea as a way to implement the file-system watcher described in https://github.com/jvilk/BrowserFS/issues/163

We could have a backend that wrapped another file system and provided hooks so you could intercept any of the method calls and add additional logic. In this scenario, I would simply intercept write, mkdir, rmdir, rename, and unlink to easily create my own "file system watcher".

ProxyFS is meant to allude to JS Proxy objects, but other names I came up with first included HookFS, WatchFS, SpyFS, or InterceptorFS.

~ @billiegoose

https://github.com/jvilk/BrowserFS/issues/196