Expose a nice wrapper for java.nio.file.Files.isX

[j-mie6]

The Files.isReadable, Files.isWritable, Files.isExecutable, etc methods would be nice to have exposed in os-lib. Something like os.isReadable, or os.is.readable would be nice.

[j-mie6]

That said, these methods don't work well if the file doesn't exist. One might assume that something like this would work more predictably:

def writable(path: os.Path): Boolean = path match {
    case parent / _ if !os.exists(path) => writable(parent)
    case path => os.exists(path) && java.nio.file.Files.isWritable(path.toNIO)
}