Utility functions for `fs`

[RiskoZoSlovenska]

Currently, besides readFile/writeFile, the fs module only provides wrappers for functions which are directly provided by luv. There are, however, some miscellaneous functions that one may find useful. The purpose of this Issue is to serve as a place to suggest and discuss them.

[RiskoZoSlovenska]

I propose the following functions, some of which have been implemented in coro-fs in Luvit 2.x.

1. fs.mkdirp(path[, mode])
2. fs.rmrf(path)
3. fs.copydir(path, newPath) (recursively copies a directory and its files/subdirectories')